LeetCode Python Solutions

A curated collection of my LeetCode solutions in Python, organized by difficulty.

Overview

This repository contains concise and interview-focused implementations for LeetCode problems.

• Language: Python
• Total solved: 64
• Difficulty split:
  • Easy: 48
  • Medium: 14
  • Hard: 2

Repository Structure

LeetCode/
|-- EasyQuestions/
|   |-- 1.py
|   |-- 13.py
|   |-- 26.py
|   |-- 27.py
|   |-- 28.py
|   |-- 66.py
|   |-- 58.py
|   |-- 9.py
|   |-- 104.py
|   |-- 111.py
|   |-- 121.py
|   |-- 125.py
|   |-- 1266.py
|   |-- 1365.py
|   |-- 1464.py
|   |-- 1480.py
|   |-- 1672.py
|   |-- 1684.py
|   |-- 1732.py
|   |-- 169.py
|   |-- 1812.py
|   |-- 1979.py
|   |-- 1929.py
|   |-- 2011.py
|   |-- 217.py
|   |-- 2235.py
|   |-- 231.py
|   |-- 2413.py
|   |-- 242.py
|   |-- 2469.py
|   |-- 2496.py
|   |-- 2582.py
|   |-- 3894.py
|   |-- 268.py
|   |-- 2769.py
|   |-- 2798.py
|   |-- 283.py
|   |-- 2894.py
|   |-- 2942.py
|   |-- 326.py
|   |-- 3274.py
|   |-- 3498.py
|   |-- 3516.py
|   |-- 3701.py
|   |-- 3110.py
|   |-- 3190.py
|   |-- 448.py
|   `-- 771.py
|-- MediumQuestions/
|   |-- 1143.py
|   |-- 17.py
|   |-- 2161.py
|   |-- 238.py
|   |-- 2433.py
|   |-- 2396.py
|   |-- 3760.py
|   |-- 39.py
|   |-- 34.py
|   |-- 49.py
|   |-- 72.py
|   |-- 75.py
|   |-- 98.py
|   `-- 153.py
`-- HardQuestions/
    |-- 4.py
    `-- 42.py

Solved Problems

#	Problem	Difficulty	File	Approach	Time	Space
1	Two Sum	Easy	EasyQuestions/1.py	One-pass hash map	O(n)	O(n)
13	Roman to Integer	Easy	EasyQuestions/13.py	Left-to-right numeral comparison	O(n)	O(1)
26	Remove Duplicates from Sorted Array	Easy	EasyQuestions/26.py	Two-pointer overwrite	O(n)	O(1)
27	Remove Element	Easy	EasyQuestions/27.py	Write-pointer compaction	O(n)	O(1)
28	Find the Index of the First Occurrence in a String	Easy	EasyQuestions/28.py	Built-in substring search	O(n*m)	O(1)
66	Plus One	Easy	EasyQuestions/66.py	Right-to-left carry handling	O(n)	O(1)
58	Length of Last Word	Easy	EasyQuestions/58.py	Strip and split string	O(n)	O(n)
9	Palindrome Number	Easy	EasyQuestions/9.py	Reverse integer and compare	O(log n)	O(1)
104	Maximum Depth of Binary Tree	Easy	EasyQuestions/104.py	DFS recursion	O(n)	O(h)
111	Minimum Depth of Binary Tree	Easy	EasyQuestions/111.py	DFS recursion with null-child handling	O(n)	O(h)
121	Best Time to Buy and Sell Stock	Easy	EasyQuestions/121.py	Track running minimum and best profit	O(n)	O(1)
125	Valid Palindrome	Easy	EasyQuestions/125.py	Filter + normalize + two-way check via reverse	O(n)	O(n)
1266	Minimum Time Visiting All Points	Easy	EasyQuestions/1266.py	Chebyshev distance accumulation	O(n)	O(1)
1365	How Many Numbers Are Smaller Than the Current Number	Easy	EasyQuestions/1365.py	Sort + first-index hash map	O(n log n)	O(n)
1464	Maximum Product of Two Elements in an Array	Easy	EasyQuestions/1464.py	Track two largest values and multiply adjusted product	O(n)	O(1)
1480	Running Sum of 1d Array	Easy	EasyQuestions/1480.py	Accumulate running sums into new array	O(n)	O(n)
1672	Richest Customer Wealth	Easy	EasyQuestions/1672.py	Row-wise sum and running maximum	O(m*n)	O(1)
1684	Count the Number of Consistent Strings	Easy	EasyQuestions/1684.py	Allowed-character set with all-check	O(n*m)	O(k)
1732	Maximum Altitude	Easy	EasyQuestions/1732.py	Iterate gains and track maximum cumulative sum	O(n)	O(1)
169	Majority Element	Easy	EasyQuestions/169.py	Boyer-Moore voting algorithm	O(n)	O(1)
1812	Determine Color of a Chessboard Square	Easy	EasyQuestions/1812.py	Parity check on file and rank	O(1)	O(1)
1979	Find Greatest Common Divisor of Array	Easy	EasyQuestions/1979.py	Euclidean algorithm on min and max	O(log n)	O(1)
1929	Concatenation of Array	Easy	EasyQuestions/1929.py	Concatenate array with itself	O(n)	O(n)
2011	Final Value of Variable After Performing Operations	Easy	EasyQuestions/2011.py	Linear simulation	O(n)	O(1)
217	Contains Duplicate	Easy	EasyQuestions/217.py	Hash set length comparison	O(n)	O(n)
2235	Add Two Integers	Easy	EasyQuestions/2235.py	Direct arithmetic addition	O(1)	O(1)
231	Power of Two	Easy	EasyQuestions/231.py	Bitwise power-of-two check	O(1)	O(1)
2413	Smallest Even Multiple	Easy	EasyQuestions/2413.py	Parity check and conditional doubling	O(1)	O(1)
242	Valid Anagram	Easy	EasyQuestions/242.py	Compare letter frequencies	O(n)	O(1)
2469	Convert the Temperature	Easy	EasyQuestions/2469.py	Direct Celsius conversion formulas	O(1)	O(1)
2582	Pass the Pillow	Easy	EasyQuestions/2582.py	Cycle-based position simulation	O(1)	O(1)
3894	Traffic Signal	Easy	EasyQuestions/3894.py	Conditional signal state lookup	O(1)	O(1)
268	Missing Number	Easy	EasyQuestions/268.py	Arithmetic sum difference	O(n)	O(1)
2769	Find the Maximum Achievable Number	Easy	EasyQuestions/2769.py	Direct arithmetic transformation	O(1)	O(1)
2798	Number of Employees Who Met the Target	Easy	EasyQuestions/2798.py	Count hours meeting or exceeding target	O(n)	O(1)
283	Move Zeroes	Easy	EasyQuestions/283.py	Two-pointer in-place swapping	O(n)	O(1)
2894	Divisible and Non-divisible Sums Difference	Easy	EasyQuestions/2894.py	Two filtered sums and subtraction	O(n)	O(1)
2942	Find Words Containing Character	Easy	EasyQuestions/2942.py	Scan words and collect matching indices	O(n*m)	O(k)
326	Power of Three	Easy	EasyQuestions/326.py	Recursive divisibility by 3	O(log n)	O(log n)
3274	Check if Two Chessboard Squares Have the Same Color	Easy	EasyQuestions/3274.py	Parity comparison of coordinate encodings	O(1)	O(1)
3498	Reverse Degree of a String	Easy	EasyQuestions/3498.py	Reverse alphabet position weighted sum	O(n)	O(1)
3516	Find Closest Person	Easy	EasyQuestions/3516.py	Compare absolute distances to target	O(1)	O(1)
3701	Alternating Sum	Easy	EasyQuestions/3701.py	Pairwise alternating addition and subtraction	O(n)	O(1)
3794	Reverse Prefix	Easy	EasyQuestions/3794.py	Reverse prefix with string slicing	O(n)	O(n)
3110	Score of a String	Easy	EasyQuestions/3110.py	Adjacent ASCII difference accumulation	O(n)	O(1)
3190	Find Minimum Operations to Make All Elements Divisible by Three	Easy	EasyQuestions/3190.py	Count non-divisible elements	O(n)	O(1)
448	Find All Numbers Disappeared in an Array	Easy	EasyQuestions/448.py	Set membership scan	O(n)	O(n)
771	Jewels and Stones	Easy	EasyQuestions/771.py	Count stones present in jewels string	O(n*m)	O(1)
17	Letter Combinations of a Phone Number	Medium	MediumQuestions/17.py	Backtracking over digit-to-letter mapping	O(4^n)	O(4^n)
2161	Partition Array According to Given Pivot	Medium	MediumQuestions/2161.py	Three lists for less/equal/greater partitions	O(n)	O(n)
39	Combination Sum	Medium	MediumQuestions/39.py	Backtracking with reusable candidates	O(2^n)	O(n)
238	Product of Array Except Self	Medium	MediumQuestions/238.py	Two-pass prefix and postfix products	O(n)	O(1)
2433	Find The Original Array of Prefix Xor	Medium	MediumQuestions/2433.py	Iterative prefix-XOR reconstruction with a preallocated array	O(n)	O(n)
2396	Strictly Palindromic Number	Medium	MediumQuestions/2396.py	Base-conversion palindrome checks with cutoff	O(log n)	O(log n)
3760	Maximum Number of Distinct Characters	Medium	MediumQuestions/3760.py	Distinct-count via hash set	O(n)	O(n)
34	Find First and Last Position of Element in Sorted Array	Medium	MediumQuestions/34.py	Two binary searches	O(log n)	O(1)
49	Group Anagrams	Medium	MediumQuestions/49.py	Character frequency signature hashing	O(n*k)	O(n*k)
72	Edit Distance	Medium	MediumQuestions/72.py	Top-down dynamic programming with memoization	O(m*n)	O(m*n)
75	Sort Colors	Medium	MediumQuestions/75.py	Dutch national flag three-pointer partition	O(n)	O(1)
98	Validate Binary Search Tree	Medium	MediumQuestions/98.py	DFS bounds validation	O(n)	O(h)
1143	Longest Common Subsequence	Medium	MediumQuestions/1143.py	Bottom-up dynamic programming table	O(m*n)	O(m*n)
153	Find Minimum in Rotated Sorted Array	Medium	MediumQuestions/153.py	Binary search on pivot side	O(log n)	O(1)
4	Median of Two Sorted Arrays	Hard	HardQuestions/4.py	Partition-based binary search	O(log(min(m, n)))	O(1)
42	Trapping Rain Water	Hard	HardQuestions/42.py	Two pointers with running boundaries	O(n)	O(1)

Run a Solution Locally

Most files contain a Solution class method matching LeetCode signatures.

1. Open the target file.
2. Add a small driver block for local testing if needed.
3. Run with Python:

python EasyQuestions/125.py

On some Windows setups, use:

py EasyQuestions/125.py

Notes

• Some files use type hints like List[int] without importing List from typing. This is fine on LeetCode if their runner accepts it, but for strict local execution you may need:

from typing import List

• Tree problems include a local TreeNode class for clarity and compatibility with LeetCode-style signatures.

Goals

• Keep solutions readable and interview-ready.
• Prefer optimal or near-optimal approaches.
• Continue expanding medium and hard coverage.

Contribution

If you want to suggest improvements:

1. Open an issue describing the optimization or bug.
2. Include input/output examples and expected complexity.
3. Keep changes focused and easy to review.

License

This repository is for learning and interview preparation. Add a license file if you plan to distribute it publicly.