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Study plan

LeetCode 75

LeetCode's own 75-problem plan, in its order: 22 topics, 22 Easy and 53 Medium, no Premium needed. Work down the list, or pick a topic. Every problem has its own page with the same steps as the schedule: learn the basics, try it on paper, code it, then a walkthrough and a tested solution in Python, Java and C++. Want the full path from scratch instead? Try the roadmap.

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0/75 solved

Easy 0/22 · Medium 0/53

Start here · Array / String

Merge Strings Alternately Easy

Array / String

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Solving on LeetCode? Connect your LeetCode username and they tick here by themselves. Solved problems come back for a quick review after 1 day, 1 week and 1 month.

1.Array / String

0/9

▶ Lesson: Static Arrays, Dynamic Arrays & Strings💡 Tip: Build strings with a list, then join

2.Two Pointers

0/4

▶ Lesson: Two Pointers in 7 Minutes💡 Tip: Two pointers from both ends of a sorted array

3.Sliding Window

0/4

▶ Lesson: Sliding Window in 7 Minutes💡 Tip: Variable windows: grow right, shrink left

4.Prefix Sum

0/2

▶ Lesson: Prefix Sum in 4 Minutes💡 Tip: Prefix sums: any range sum in O(1)

5.Hash Map / Set

0/4

▶ Lesson: HashMaps & Dictionaries, Explained Simply💡 Tip: Counting things with a hash map

6.Stack

0/3

▶ Lesson: Stacks & Queues💡 Tip: Matching brackets with a stack

7.Queue

0/2

▶ Lesson: Stacks & Queues

8.Linked List

0/4

▶ Lesson: Linked Lists: Singly & Doubly Linked💡 Tip: Reversing a linked list without losing it

9.Binary Tree: DFS

0/6

▶ Lesson: Binary Trees & Binary Search Trees💡 Tip: Thinking recursively about trees

10.Binary Tree: BFS

0/2

▶ Lesson: DFS vs BFS, When to Use Which?💡 Tip: BFS level by level

11.Binary Search Tree

0/2

▶ Lesson: Binary Trees & Binary Search Trees

12.Graphs: DFS

0/4

▶ Lesson: Graphs: Adjacency Lists, DFS & BFS💡 Tip: A grid is a graph: counting islands with DFS

13.Graphs: BFS

0/2

▶ Lesson: DFS vs BFS, When to Use Which?💡 Tip: Shortest path in a grid is BFS

14.Heap / Priority Queue

0/4

▶ Lesson: Heaps & Priority Queues (heapq)💡 Tip: Top K with a small heap

16.Backtracking

0/2

▶ Lesson: Solve Any Backtracking Problem (Template)💡 Tip: Backtracking: choose, explore, un-choose

17.DP: 1D

0/4

▶ Lesson: Mastering Dynamic Programming💡 Tip: Dynamic programming starts with one sentence

18.DP: Multidimensional

0/4

▶ Lesson: Mastering Dynamic Programming💡 Tip: 2-D DP: a grid of subproblems

19.Bit Manipulation

0/3

▶ Lesson: Introduction to Bit Manipulation💡 Tip: Three bit tricks worth knowing

20.Trie

0/2

▶ Lesson: Implement Trie: Insert, Search, StartsWith💡 Tip: Tries for prefix questions

21.Intervals

0/2

▶ Lesson: Merge Overlapping Intervals💡 Tip: Intervals: sort by start, then sweep

22.Monotonic Stack

0/2

▶ Lesson: Stacks & Queues💡 Tip: Monotonic stack: the next greater element