Web Push CenterApple APNs & Web Push

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Real-time push delivery to your iPhone Home Screen PWA. Alarms fire at 09:00, 12:00, 15:00, and 18:00 in your local timezone.

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630 tasks

Coding Day 2

LC 76 Minimum Window Substring

System design Day 2

Consistent hashing

Estimation Day 2

Partitions when N → N+1

Coding Day 1

Two Sum + 3Sum

Coding Day 1

Two Sum + 3Sum

Coding Day 1

Maximum Subarray / Kadane

Coding Day 1

Maximum Subarray / Kadane

System design Day 1

L4 vs L7 load balancing

System design Day 1

L4 vs L7 load balancing

System design Day 1

RR vs least-conn vs IP-hash

System design Day 1

RR vs least-conn vs IP-hash

Coding Day 3

Trapping Rain Water

System design Day 3

Reverse proxy vs API gateway

Estimation Day 3

QPS behind one L7 proxy

Coding Day 2

LC 3 Longest Unique Substring

Coding Day 2

LC 3 Longest Unique Substring

Coding Day 2

LC 76 Minimum Window Substring

Coding Day 2

LC 76 Minimum Window Substring

System design Day 2

Consistent hashing

System design Day 2

Consistent hashing

Estimation Day 2

Partitions when N → N+1

Estimation Day 2

Partitions when N → N+1

Coding Day 4

Longest Consecutive Sequence

System design Day 4

CAP in one minute

System design Day 4

Strong vs eventual consistency

Coding Day 3

Container With Most Water

Coding Day 3

Container With Most Water

Coding Day 3

Trapping Rain Water

Coding Day 3

Trapping Rain Water

System design Day 3

Reverse proxy vs API gateway

System design Day 3

Reverse proxy vs API gateway

Estimation Day 3

QPS behind one L7 proxy

Estimation Day 3

QPS behind one L7 proxy

Coding Day 5

Palindrome + Longest Palindrome

System design Day 5

DNS, TLS, request path

Estimation Day 5

1M × 2KB JSON requests/s

Coding Day 4

Subarray Sum Equals K

Coding Day 4

Subarray Sum Equals K

Coding Day 4

Longest Consecutive Sequence

Coding Day 4

Longest Consecutive Sequence

System design Day 4

CAP in one minute

System design Day 4

CAP in one minute

System design Day 4

Strong vs eventual consistency

System design Day 4

Strong vs eventual consistency

Coding Day 6

Daily Temperatures

Coding Day 6

Largest Rectangle in Histogram

System design Day 6

Health checks and failover

Coding Day 5

Group Anagrams

Coding Day 5

Group Anagrams

Coding Day 5

Palindrome + Longest Palindrome

Coding Day 5

Palindrome + Longest Palindrome

System design Day 5

DNS, TLS, request path

System design Day 5

DNS, TLS, request path

Estimation Day 5

1M × 2KB JSON requests/s

Estimation Day 5

1M × 2KB JSON requests/s

Coding Day 7

Redo the weakest problem timed

Admin Day 7

Tag 3 pattern gaps for week 2

Coding Day 6

Valid Parentheses + Min Stack

Coding Day 6

Valid Parentheses + Min Stack

Coding Day 6

Daily Temperatures

Coding Day 6

Daily Temperatures

Coding Day 6

Largest Rectangle in Histogram

Coding Day 6

Largest Rectangle in Histogram

System design Day 6

Health checks and failover

System design Day 6

Health checks and failover

Coding Day 8

Cycle + Intersection

System design Day 8

Write-through vs write-back

System design Day 8

LRU vs LFU eviction

Coding Day 7

Redo the weakest problem timed

Coding Day 7

Redo the weakest problem timed

Admin Day 7

Tag 3 pattern gaps for week 2

Admin Day 7

Tag 3 pattern gaps for week 2

Coding Day 9

Merge K Sorted Lists

Coding Day 9

Top K Frequent Elements

System design Day 9

Redis as cache vs primary

Coding Day 8

Reverse List / Reverse K-Group

Coding Day 8

Reverse List / Reverse K-Group

Coding Day 8

Cycle + Intersection

Coding Day 8

Cycle + Intersection

System design Day 8

Write-through vs write-back

System design Day 8

Write-through vs write-back

System design Day 8

LRU vs LFU eviction

System design Day 8

LRU vs LFU eviction

Coding Day 10

Insert Interval

Coding Day 10

Meeting Rooms II

Estimation Day 10

Calendar fan-out, 10k meetings

Coding Day 9

Kth Largest Element

Coding Day 9

Kth Largest Element

Coding Day 9

Merge K Sorted Lists

Coding Day 9

Merge K Sorted Lists

Coding Day 9

Top K Frequent Elements

Coding Day 9

Top K Frequent Elements

System design Day 9

Redis as cache vs primary

System design Day 9

Redis as cache vs primary

Coding Day 11

Find Peak Element

Coding Day 11

Time-Based Key-Value Store

System design Day 11

Binary search over logs

Coding Day 10

Merge Intervals

Coding Day 10

Merge Intervals

Coding Day 10

Insert Interval

Coding Day 10

Insert Interval

Coding Day 10

Meeting Rooms II

Coding Day 10

Meeting Rooms II

Estimation Day 10

Calendar fan-out, 10k meetings

Estimation Day 10

Calendar fan-out, 10k meetings

System design Day 12

CDN vs origin cache

Coding Day 12

LRU Cache

Estimation Day 12

Hit rate needed to hold p99

Coding Day 11

Search Rotated Array

Coding Day 11

Search Rotated Array

Coding Day 11

Find Peak Element

Coding Day 11

Find Peak Element

Coding Day 11

Time-Based Key-Value Store

Coding Day 11

Time-Based Key-Value Store

System design Day 11

Binary search over logs

System design Day 11

Binary search over logs

System design Day 13

Competing consumers, poison pills

Coding Day 13

Sliding Window Maximum

LLD Day 13

Bounded blocking queue

System design Day 12

Cache aside, stampede, TTL

System design Day 12

Cache aside, stampede, TTL

System design Day 12

CDN vs origin cache

System design Day 12

CDN vs origin cache

Coding Day 12

LRU Cache

Coding Day 12

LRU Cache

Estimation Day 12

Hit rate needed to hold p99

Estimation Day 12

Hit rate needed to hold p99

Coding Day 14

Timed medium from week 2

Admin Day 14

Draft 5 STAR story titles

System design Day 13

At-least-once vs exactly-once

System design Day 13

At-least-once vs exactly-once

System design Day 13

Competing consumers, poison pills

System design Day 13

Competing consumers, poison pills

Coding Day 13

Sliding Window Maximum

Coding Day 13

Sliding Window Maximum

LLD Day 13

Bounded blocking queue

LLD Day 13

Bounded blocking queue

Coding Day 15

Lowest Common Ancestor

Coding Day 15

Serialize / Deserialize Tree

System design Day 15

Blob vs block vs object store

Coding Day 14

Timed medium from week 2

Coding Day 14

Timed medium from week 2

Admin Day 14

Draft 5 STAR story titles

Admin Day 14

Draft 5 STAR story titles

Coding Day 16

Kth Smallest in BST

Coding Day 16

Binary Tree Max Path Sum

Behavioral Day 16

STAR — owned a technical mistake

Coding Day 15

Level Order + Zigzag

Coding Day 15

Level Order + Zigzag

Coding Day 15

Lowest Common Ancestor

Coding Day 15

Lowest Common Ancestor

Coding Day 15

Serialize / Deserialize Tree

Coding Day 15

Serialize / Deserialize Tree

System design Day 15

Blob vs block vs object store

System design Day 15

Blob vs block vs object store

Coding Day 17

Clone Graph

Coding Day 17

Word Ladder

System design Day 17

Service discovery

Coding Day 16

Validate BST

Coding Day 16

Validate BST

Coding Day 16

Kth Smallest in BST

Coding Day 16

Kth Smallest in BST

Coding Day 16

Binary Tree Max Path Sum

Coding Day 16

Binary Tree Max Path Sum

Behavioral Day 16

STAR — owned a technical mistake

Behavioral Day 16

STAR — owned a technical mistake

Coding Day 18

Connected Components

Coding Day 18

Accounts Merge

System design Day 18

Circuit breaker, retry, timeout

Coding Day 17

Number of Islands

Coding Day 17

Number of Islands

Coding Day 17

Clone Graph

Coding Day 17

Clone Graph

Coding Day 17

Word Ladder

Coding Day 17

Word Ladder

System design Day 17

Service discovery

System design Day 17

Service discovery

System design Day 19

Global limiter, multi-region

Estimation Day 19

100k rps counters, 1% error

LLD Day 19

RateLimiter class API

Coding Day 18

Course Schedule I / II

Coding Day 18

Course Schedule I / II

Coding Day 18

Connected Components

Coding Day 18

Connected Components

Coding Day 18

Accounts Merge

Coding Day 18

Accounts Merge

System design Day 18

Circuit breaker, retry, timeout

System design Day 18

Circuit breaker, retry, timeout

System design Day 20

Aliases, analytics, abuse

Estimation Day 20

100M new URLs / month

Coding Day 20

Encode and Decode TinyURL

System design Day 19

Token bucket vs sliding window

System design Day 19

Token bucket vs sliding window

System design Day 19

Global limiter, multi-region

System design Day 19

Global limiter, multi-region

Estimation Day 19

100k rps counters, 1% error

Estimation Day 19

100k rps counters, 1% error

LLD Day 19

RateLimiter class API

LLD Day 19

RateLimiter class API

Mock Day 21

45-min coding mock, tree or graph

Admin Day 21

Update the pattern gap list

System design Day 20

TinyURL — IDs, 301 vs 302

System design Day 20

TinyURL — IDs, 301 vs 302

System design Day 20

Aliases, analytics, abuse

System design Day 20

Aliases, analytics, abuse

Estimation Day 20

100M new URLs / month

Estimation Day 20

100M new URLs / month

Coding Day 20

Encode and Decode TinyURL

Coding Day 20

Encode and Decode TinyURL

Coding Day 22

Coin Change

Coding Day 22

Longest Increasing Subsequence

System design Day 22

SQL vs NoSQL decision tree

Mock Day 21

45-min coding mock, tree or graph

Mock Day 21

45-min coding mock, tree or graph

Admin Day 21

Update the pattern gap list

Admin Day 21

Update the pattern gap list

Coding Day 23

Edit Distance

Coding Day 23

Longest Common Subsequence

Estimation Day 23

1B rows, 200 B, 3 replicas

Coding Day 22

House Robber I / II

Coding Day 22

House Robber I / II

Coding Day 22

Coin Change

Coding Day 22

Coin Change

Coding Day 22

Longest Increasing Subsequence

Coding Day 22

Longest Increasing Subsequence

System design Day 22

SQL vs NoSQL decision tree

System design Day 22

SQL vs NoSQL decision tree

Coding Day 24

Word Search

Coding Day 24

N-Queens — prune narration

Behavioral Day 24

STAR — stakeholder disagreement

Coding Day 23

Unique Paths

Coding Day 23

Unique Paths

Coding Day 23

Edit Distance

Coding Day 23

Edit Distance

Coding Day 23

Longest Common Subsequence

Coding Day 23

Longest Common Subsequence

Estimation Day 23

1B rows, 200 B, 3 replicas

Estimation Day 23

1B rows, 200 B, 3 replicas

Coding Day 25

Cheapest Flights K Stops

Coding Day 25

Alien Dictionary

System design Day 25

Sharding: hash, range, geo

Coding Day 24

Combination Sum

Coding Day 24

Combination Sum

Coding Day 24

Word Search

Coding Day 24

Word Search

Coding Day 24

N-Queens — prune narration

Coding Day 24

N-Queens — prune narration

Behavioral Day 24

STAR — stakeholder disagreement

Behavioral Day 24

STAR — stakeholder disagreement

System design Day 26

Ranking, fan-out, celebrities

Estimation Day 26

Fan-out for 10M DAU

Coding Day 26

Design Twitter

Coding Day 25

Network Delay Time

Coding Day 25

Network Delay Time

Coding Day 25

Cheapest Flights K Stops

Coding Day 25

Cheapest Flights K Stops

Coding Day 25

Alien Dictionary

Coding Day 25

Alien Dictionary

System design Day 25

Sharding: hash, range, geo

System design Day 25

Sharding: hash, range, geo

System design Day 27

Presence, receipts, groups

Estimation Day 27

50M concurrent WebSockets

LLD Day 27

Message store schema + API

System design Day 26

Feed — push vs pull

System design Day 26

Feed — push vs pull

System design Day 26

Ranking, fan-out, celebrities

System design Day 26

Ranking, fan-out, celebrities

Estimation Day 26

Fan-out for 10M DAU

Estimation Day 26

Fan-out for 10M DAU

Coding Day 26

Design Twitter

Coding Day 26

Design Twitter

Mock Day 28

60-min SD mock: shortener or limiter

Admin Day 28

Pick 2 SD prompts to repeat

System design Day 27

WhatsApp-style chat

System design Day 27

WhatsApp-style chat

System design Day 27

Presence, receipts, groups

System design Day 27

Presence, receipts, groups

Estimation Day 27

50M concurrent WebSockets

Estimation Day 27

50M concurrent WebSockets

LLD Day 27

Message store schema + API

LLD Day 27

Message store schema + API

System design Day 29

Priority, batching, quiet hours

Estimation Day 29

1B pushes/day, p99 < 5s

Coding Day 29

Design Hit Counter

Mock Day 28

60-min SD mock: shortener or limiter

Mock Day 28

60-min SD mock: shortener or limiter

Admin Day 28

Pick 2 SD prompts to repeat

Admin Day 28

Pick 2 SD prompts to repeat

System design Day 30

Inverted index, ranking, freshness

Estimation Day 30

Index size, 100M docs × 2KB

LLD Day 30

Trie vs inverted index

System design Day 29

Push, email, in-app notifications

System design Day 29

Push, email, in-app notifications

System design Day 29

Priority, batching, quiet hours

System design Day 29

Priority, batching, quiet hours

Estimation Day 29

1B pushes/day, p99 < 5s

Estimation Day 29

1B pushes/day, p99 < 5s

Coding Day 29

Design Hit Counter

Coding Day 29

Design Hit Counter

System design Day 31

Scan, thumbnails, invalidation

Estimation Day 31

10M uploads/day, 2MB avg

LLD Day 31

Asset metadata model

System design Day 30

Typeahead / autocomplete

System design Day 30

Typeahead / autocomplete

System design Day 30

Inverted index, ranking, freshness

System design Day 30

Inverted index, ranking, freshness

Estimation Day 30

Index size, 100M docs × 2KB

Estimation Day 30

Index size, 100M docs × 2KB

LLD Day 30

Trie vs inverted index

LLD Day 30

Trie vs inverted index

System design Day 32

AuthN / AuthZ, tokens, sessions

Estimation Day 32

Token validation at 200k rps

Behavioral Day 32

STAR — ambiguous requirements

System design Day 31

Image upload → blob → CDN

System design Day 31

Image upload → blob → CDN

System design Day 31

Scan, thumbnails, invalidation

System design Day 31

Scan, thumbnails, invalidation

Estimation Day 31

10M uploads/day, 2MB avg

Estimation Day 31

10M uploads/day, 2MB avg

LLD Day 31

Asset metadata model

LLD Day 31

Asset metadata model

LLD Day 33

Parking Lot — tickets and fees

Coding Day 33

Min Stack + Max Freq Stack

System design Day 33

When LLD becomes HLD in the room

System design Day 32

Shared vs silo isolation

System design Day 32

Shared vs silo isolation

System design Day 32

AuthN / AuthZ, tokens, sessions

System design Day 32

AuthN / AuthZ, tokens, sessions

Estimation Day 32

Token validation at 200k rps

Estimation Day 32

Token validation at 200k rps

Behavioral Day 32

STAR — ambiguous requirements

Behavioral Day 32

STAR — ambiguous requirements

LLD Day 34

Elevator system

Coding Day 34

Task Scheduler (LC 621)

Estimation Day 34

Workers for 5k jobs/min

LLD Day 33

LRU Cache — code + concurrency

LLD Day 33

LRU Cache — code + concurrency

LLD Day 33

Parking Lot — tickets and fees

LLD Day 33

Parking Lot — tickets and fees

Coding Day 33

Min Stack + Max Freq Stack

Coding Day 33

Min Stack + Max Freq Stack

System design Day 33

When LLD becomes HLD in the room

System design Day 33

When LLD becomes HLD in the room

Mock Day 35

60-min SD mock: notify or search

Admin Day 35

8-story STAR bank checklist

LLD Day 34

Task scheduler / thread pool

LLD Day 34

Task scheduler / thread pool

LLD Day 34

Elevator system

LLD Day 34

Elevator system

Coding Day 34

Task Scheduler (LC 621)

Coding Day 34

Task Scheduler (LC 621)

Estimation Day 34

Workers for 5k jobs/min

Estimation Day 34

Workers for 5k jobs/min

Behavioral Day 36

Story — incident you caused

Behavioral Day 36

Story — mentored / raised the bar

Admin Day 36

Quantify impact numbers

Mock Day 35

60-min SD mock: notify or search

Mock Day 35

60-min SD mock: notify or search

Admin Day 35

8-story STAR bank checklist

Admin Day 35

8-story STAR bank checklist

Behavioral Day 37

Story — shipped imperfect, right call

Behavioral Day 37

Map stories to growth-mindset rubric

Coding Day 37

20-min timed warm-up medium

Behavioral Day 36

Story — cross-team influence

Behavioral Day 36

Story — cross-team influence

Behavioral Day 36

Story — incident you caused

Behavioral Day 36

Story — incident you caused

Behavioral Day 36

Story — mentored / raised the bar

Behavioral Day 36

Story — mentored / raised the bar

Admin Day 36

Quantify impact numbers

Admin Day 36

Quantify impact numbers

Behavioral Day 38

Story — customer-framed technical bet

Behavioral Day 38

Practice 2-minute versions out loud

System design Day 38

10x load pass on last design

Behavioral Day 37

Story — learned something fundamental

Behavioral Day 37

Story — learned something fundamental

Behavioral Day 37

Story — shipped imperfect, right call

Behavioral Day 37

Story — shipped imperfect, right call

Behavioral Day 37

Map stories to growth-mindset rubric

Coding Day 1

Two Sum + 3Sum

Behavioral Day 37

Map stories to growth-mindset rubric

Coding Day 37

20-min timed warm-up medium

Coding Day 1

Maximum Subarray / Kadane

Coding Day 37

20-min timed warm-up medium

Estimation Day 39

Teams presence, 300M MAU

System design Day 1

L4 vs L7 load balancing

Estimation Day 39

Latency cheat sheet from memory

System design Day 1

RR vs least-conn vs IP-hash

Coding Day 39

Random LC medium, narrate first

Behavioral Day 38

Story — conflict with PM or peer

Behavioral Day 38

Story — conflict with PM or peer

Behavioral Day 38

Story — customer-framed technical bet

Behavioral Day 38

Story — customer-framed technical bet

Behavioral Day 38

Practice 2-minute versions out loud

Coding Day 2

LC 3 Longest Unique Substring

Behavioral Day 38

Practice 2-minute versions out loud

System design Day 38

10x load pass on last design

Coding Day 2

LC 76 Minimum Window Substring

System design Day 38

10x load pass on last design

LLD Day 40

In-process pub-sub

System design Day 2

Consistent hashing

LLD Day 40

Chess or deck of cards

Estimation Day 2

Partitions when N → N+1

Coding Day 40

Implement Trie

Estimation Day 39

YouTube-lite: QPS, store, pipe

Estimation Day 39

YouTube-lite: QPS, store, pipe

Estimation Day 39

Teams presence, 300M MAU

Estimation Day 39

Teams presence, 300M MAU

Estimation Day 39

Latency cheat sheet from memory

Coding Day 3

Container With Most Water

Estimation Day 39

Latency cheat sheet from memory

Coding Day 39

Random LC medium, narrate first

Coding Day 3

Trapping Rain Water

Coding Day 39

Random LC medium, narrate first

System design Day 41

Scope a design in 8 minutes

System design Day 3

Reverse proxy vs API gateway

Behavioral Day 41

One story with interruptions

Estimation Day 3

QPS behind one L7 proxy

Admin Day 41

Loop logistics checklist

LLD Day 40

Logger / rate-limited logger

LLD Day 40

Logger / rate-limited logger

LLD Day 40

In-process pub-sub

LLD Day 40

In-process pub-sub

LLD Day 40

Chess or deck of cards

Coding Day 4

Subarray Sum Equals K

LLD Day 40

Chess or deck of cards

Coding Day 40

Implement Trie

Coding Day 4

Longest Consecutive Sequence

Coding Day 40

Implement Trie

Mock Day 42

45-min behavioral mock

System design Day 4

CAP in one minute

Admin Day 42

Cut IC-scope stories

System design Day 4

Strong vs eventual consistency

Coding Day 41

Medium + ‘now 10M rows’ follow-up

Coding Day 41

Medium + ‘now 10M rows’ follow-up

System design Day 41

Scope a design in 8 minutes

System design Day 41

Scope a design in 8 minutes

Behavioral Day 41

One story with interruptions

Coding Day 5

Group Anagrams

Behavioral Day 41

One story with interruptions

Admin Day 41

Loop logistics checklist

Coding Day 5

Palindrome + Longest Palindrome

Admin Day 41

Loop logistics checklist

Coding Day 43

Post-mock: edges you missed

System design Day 5

DNS, TLS, request path

Coding Day 43

Re-solve the mock problem clean

Estimation Day 5

1M × 2KB JSON requests/s

Admin Day 43

Score narration, not just AC

Mock Day 42

45-min behavioral mock

Mock Day 42

45-min behavioral mock

Admin Day 42

Cut IC-scope stories

Coding Day 6

Valid Parentheses + Min Stack

Admin Day 42

Cut IC-scope stories

Coding Day 6

Daily Temperatures

Coding Day 44

Follow-up: scale the solution to 10M

Coding Day 6

Largest Rectangle in Histogram

LLD Day 44

If they pivot to class design, 20 min

System design Day 6

Health checks and failover

Mock Day 43

60-min coding mock — arrays/windows

Mock Day 43

60-min coding mock — arrays/windows

Coding Day 43

Post-mock: edges you missed

Coding Day 43

Post-mock: edges you missed

Coding Day 43

Re-solve the mock problem clean

Coding Day 43

Re-solve the mock problem clean

Admin Day 43

Score narration, not just AC

Coding Day 7

Redo the weakest problem timed

Admin Day 43

Score narration, not just AC

Estimation Day 45

Redo the numbers cold

Admin Day 7

Tag 3 pattern gaps for week 2

System design Day 45

Failure modes and SLOs

Admin Day 45

Azure primitives you named

Mock Day 44

60-min coding mock — graphs/trees

Mock Day 44

60-min coding mock — graphs/trees

Coding Day 44

Follow-up: scale the solution to 10M

Coding Day 44

Follow-up: scale the solution to 10M

LLD Day 44

If they pivot to class design, 20 min

Coding Day 8

Reverse List / Reverse K-Group

LLD Day 44

If they pivot to class design, 20 min

Coding Day 8

Cycle + Intersection

LLD Day 46

Concurrency and tests

System design Day 8

Write-through vs write-back

Coding Day 46

One LC design problem

System design Day 8

LRU vs LFU eviction

Behavioral Day 46

10-min story if they weave it in

Mock Day 45

60-min SD — limiter or chat

Mock Day 45

60-min SD — limiter or chat

Estimation Day 45

Redo the numbers cold

Estimation Day 45

Redo the numbers cold

System design Day 45

Failure modes and SLOs

Coding Day 9

Kth Largest Element

System design Day 45

Failure modes and SLOs

Admin Day 45

Azure primitives you named

Coding Day 9

Merge K Sorted Lists

Admin Day 45

Azure primitives you named

Behavioral Day 47

Senior-skip probe on weakest story

Coding Day 9

Top K Frequent Elements

Admin Day 47

Rewrite one story with larger scope

System design Day 9

Redis as cache vs primary

Coding Day 47

Light 20-min to keep the hand warm

Mock Day 46

45-min LLD — lot or scheduler

Mock Day 46

45-min LLD — lot or scheduler

LLD Day 46

Concurrency and tests

LLD Day 46

Concurrency and tests

Coding Day 46

One LC design problem

Coding Day 10

Merge Intervals

Coding Day 46

One LC design problem

Behavioral Day 46

10-min story if they weave it in

Coding Day 10

Insert Interval

Behavioral Day 46

10-min story if they weave it in

Mock Day 48

System design 50 min

Coding Day 10

Meeting Rooms II

Estimation Day 10

Calendar fan-out, 10k meetings

Admin Day 48

Sleep and nutrition for loop week

Mock Day 47

45-min behavioral mock

Mock Day 47

45-min behavioral mock

Behavioral Day 47

Senior-skip probe on weakest story

Behavioral Day 47

Senior-skip probe on weakest story

Admin Day 47

Rewrite one story with larger scope

Coding Day 11

Search Rotated Array

Admin Day 47

Rewrite one story with larger scope

Coding Day 47

Light 20-min to keep the hand warm

Coding Day 11

Find Peak Element

Coding Day 47

Light 20-min to keep the hand warm

Admin Day 49

Top 5 remaining gaps

Coding Day 11

Time-Based Key-Value Store

Coding Day 49

Drill the #1 coding gap only

System design Day 11

Binary search over logs

Mock Day 48

Coding 50 min

Mock Day 48

Coding 50 min

Mock Day 48

System design 50 min

Mock Day 48

System design 50 min

System design Day 12

Cache aside, stampede, TTL

Admin Day 48

Sleep and nutrition for loop week

System design Day 12

CDN vs origin cache

Admin Day 48

Sleep and nutrition for loop week

Mock Day 50

Coding round 2 (60)

Coding Day 12

LRU Cache

Estimation Day 12

Hit rate needed to hold p99

Admin Day 50

No new topics unless a hole is fatal

Admin Day 49

Top 5 remaining gaps

Admin Day 49

Top 5 remaining gaps

System design Day 13

At-least-once vs exactly-once

Coding Day 49

Drill the #1 coding gap only

Mock Day 51

System design 60

System design Day 13

Competing consumers, poison pills

Mock Day 51

Behavioral 45

Coding Day 13

Sliding Window Maximum

LLD Day 13

Bounded blocking queue

Estimation Day 51

10-min numbers recap

Mock Day 50

Coding round 1 (60)

Mock Day 50

Coding round 1 (60)

Mock Day 50

Coding round 2 (60)

Mock Day 50

Coding round 2 (60)

Coding Day 52

Weak pattern — problem 1

Coding Day 14

Timed medium from week 2

Admin Day 50

No new topics unless a hole is fatal

Coding Day 52

Weak pattern — problem 2

Admin Day 14

Draft 5 STAR story titles

System design Day 52

Resketch the design you botched

Behavioral Day 52

2-minute story fire drill ×3

Mock Day 51

System design 60

Mock Day 51

System design 60

Mock Day 51

Behavioral 45

Mock Day 51

Behavioral 45

Coding Day 15

Level Order + Zigzag

LLD Day 53

One clean LLD from memory

Coding Day 15

Lowest Common Ancestor

Estimation Day 51

10-min numbers recap

Estimation Day 53

Three prompts, 8 min each

Coding Day 15

Serialize / Deserialize Tree

Coding Day 53

Two mediums, approach-first

System design Day 15

Blob vs block vs object store

Admin Day 53

Questions to ask interviewers

Coding Day 52

Weak pattern — problem 1

Coding Day 52

Weak pattern — problem 1

Coding Day 52

Weak pattern — problem 2

Coding Day 52

Weak pattern — problem 2

Coding Day 16

Validate BST

System design Day 52

Resketch the design you botched

Coding Day 54

One familiar medium, perfect talk

Coding Day 16

Kth Smallest in BST

Behavioral Day 52

2-minute story fire drill ×3

Behavioral Day 54

Read STAR bank once out loud

Coding Day 16

Binary Tree Max Path Sum

System design Day 54

15-min high-level of a known prompt

Behavioral Day 16

STAR — owned a technical mistake

Admin Day 54

Logistics — ID, Teams, timezone

LLD Day 53

One clean LLD from memory

LLD Day 53

One clean LLD from memory

Estimation Day 53

Three prompts, 8 min each

Estimation Day 53

Three prompts, 8 min each

Coding Day 17

Number of Islands

Coding Day 53

Two mediums, approach-first

Coding Day 17

Clone Graph

Admin Day 53

Questions to ask interviewers

Admin Day 55

Skim cheat sheets only

Coding Day 17

Word Ladder

Behavioral Day 55

One story if anxiety spikes

System design Day 17

Service discovery

Coding Day 54

One familiar medium, perfect talk

Coding Day 54

One familiar medium, perfect talk

Behavioral Day 54

Read STAR bank once out loud

Behavioral Day 54

Read STAR bank once out loud

Coding Day 18

Course Schedule I / II

System design Day 54

15-min high-level of a known prompt

Coding Day 18

Connected Components

Admin Day 54

Logistics — ID, Teams, timezone

Admin Day 56

Loop-day runbook

Coding Day 18

Accounts Merge

System design Day 18

Circuit breaker, retry, timeout

Admin Day 55

Skim cheat sheets only

Admin Day 55

Skim cheat sheets only

System design Day 19

Token bucket vs sliding window

Behavioral Day 55

One story if anxiety spikes

System design Day 19

Global limiter, multi-region

Estimation Day 19

100k rps counters, 1% error

LLD Day 19

RateLimiter class API

Admin Day 56

Loop-day runbook

Admin Day 56

Loop-day runbook

System design Day 20

TinyURL — IDs, 301 vs 302

System design Day 20

Aliases, analytics, abuse

Estimation Day 20

100M new URLs / month

Coding Day 20

Encode and Decode TinyURL

Mock Day 21

45-min coding mock, tree or graph

Admin Day 21

Update the pattern gap list

Coding Day 22

House Robber I / II

Coding Day 22

Coin Change

Coding Day 22

Longest Increasing Subsequence

System design Day 22

SQL vs NoSQL decision tree

Coding Day 23

Unique Paths

Upcoming Schedule

Next 30 reminders

Day 23

Edit Distance

Day 23

Longest Common Subsequence

Day 23

1B rows, 200 B, 3 replicas

Day 24

Combination Sum

Day 24

Word Search

Day 24

N-Queens — prune narration

Day 24

STAR — stakeholder disagreement

Day 25

Network Delay Time

Day 25

Cheapest Flights K Stops

Day 25

Alien Dictionary

Day 25

Sharding: hash, range, geo

Day 26

Feed — push vs pull

Day 26

Ranking, fan-out, celebrities

Day 26

Fan-out for 10M DAU

Day 26

Design Twitter

Day 27

WhatsApp-style chat

Day 27

Presence, receipts, groups

Day 27

50M concurrent WebSockets

Day 27

Message store schema + API

Day 28

60-min SD mock: shortener or limiter

Day 28

Pick 2 SD prompts to repeat

Day 29

Push, email, in-app notifications

Day 29

Priority, batching, quiet hours

Day 29

1B pushes/day, p99 < 5s

Day 29

Design Hit Counter

Day 30

Typeahead / autocomplete

Day 30

Inverted index, ranking, freshness

Day 30

Index size, 100M docs × 2KB

Day 30

Trie vs inverted index

Day 31

Image upload → blob → CDN

iPhone APNs Flow

Add to Home Screen from Safari on iOS 16.4+.
Launch PWA icon and tap Enable Notifications.
Server cron evaluates v_due_reminders and dispatches Web Push payload via Apple APNs.
iPhone lock screen renders notification banner. Tapping opens today’s study session.

· Tag/Identifier: reminder.id

· Times follow the timezone of this device

· Retro tasks remain silent

Push Payload Contract

tagreminder.id

senderGET/POST /api/cron/due-reminders

channelweb_push

not_smstrue

categoryTASK_REMIND

requires["iOS 16.4+","Add to Home Screen","Open from home-screen icon","Enable notifications (user tap)","HTTPS"]

subscribePOST /api/push/subscribe

identifierreminder.id::text

ios_actionstap opens PWA — Complete / Snooze are in-app (iOS Web Push has no lock-screen action buttons)

desktop_actions[{"id":"complete","title":"Complete","effect":"SET tasks.is_done = true"},{"id":"snooze_1h","title":"Snooze 1h","effect":"INSERT reminder fire_at = now() + interval '1 hour'"}]

skip_if_task_donetrue