Leetcode

Find all my leetcode problem solving notes

I collated all the leetcode problems i solved in here so you can learn from it

23 Oct 2025•Python•Medium

Unique Paths II

count paths from top-left to bottom-right with obstacles using dp with space optimization to O(n).

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23 Oct 2025•TypeScript•Medium

Wiggle Sort II

rearrange array in wiggle pattern (nums[0] < nums[1] > nums[2] < ...) using sorted interleaving.

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14 Oct 2025•TypeScript•Medium

Largest Plus Sign

find the largest plus sign order by computing longest consecutive 1s in four directions using dp.

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03 Sept 2025•Python•Hard

Zuma Game

find minimum balls needed to clear board using dfs with memoization, trying to form groups of 3+.

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26 Aug 2025•Python•Hard

Candy

distribute candy to children based on ratings using two-pass greedy approach.

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24 Apr 2025•TypeScript•Hard

LFU Cache

implement least frequently used cache with O(1) operations using hash maps and doubly linked lists.

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24 Apr 2025•Python•Hard

Word Ladder

find shortest transformation sequence from beginWord to endWord using bfs.

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21 Mar 2025•Python•Hard

Palindrome Pairs

find all pairs of words that form palindrome when concatenated by checking all prefix/suffix splits.

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01 Feb 2025•PHP•Hard

Valid Number

validate if string represents a valid number using state machine or regex.

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20 Sept 2024•C•Medium

Set Matrix Zeroes

set entire row and column to zero when element is zero, using first row and column as markers for O(1) space.

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16 Jul 2024•TypeScript•Hard

Stamping the Grid

check if a grid can be fully covered by stamps using prefix sums and 2d difference array.

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30 Jun 2024•PHP•Hard

Number of Digit One

count total number of digit 1 appearing in all numbers from 1 to n using digit dp or mathematical analysis.

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06 Jun 2024•PHP•Hard

Word Ladder II

find all shortest transformation sequences from beginWord to endWord using bfs with path tracking.

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03 May 2024•TypeScript•Medium

String Compression

compress string in-place by replacing consecutive characters with character and count using two pointers.

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17 Apr 2024•Python•Hard

Perfect Rectangle

check if rectangles form exact rectangle without gaps or overlaps using corner counting and area validation.

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27 Feb 2024•TypeScript•Hard

Frog Jump

determine if a frog can cross a river using dfs with memoization, tracking position and last jump distance.

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17 Jan 2024•PHP•Hard

Contains Duplicate III

check if there exist two indices with value difference ≤ valueDiff and index difference ≤ indexDiff using sliding window with sorted array.

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03 Nov 2023•Python•Hard

Reverse Pairs

count pairs where nums[i] > 2 * nums[j] and i < j using merge sort with counting during merge phase.

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04 Aug 2023•Python•Medium

Minimum Path Sum

find minimum sum path from top-left to bottom-right using dynamic programming with space optimization.

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27 Jul 2023•Python•Medium

Building H2O

coordinate hydrogen and oxygen threads to form water molecules using semaphores and barrier synchronization.

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24 Jun 2023•Python•Easy

Two Sum

find two indices whose values sum to target using hash map for O(n) lookup.

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16 Jun 2023•PHP•Hard

First Missing Positive

find the smallest missing positive integer using array as hash table by placing each number at its correct index.

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17 Jan 2023•TypeScript•Medium

Simplify Path

normalize unix-style file paths by handling . and .. components using a stack.

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