DSA-Problems

LeetCode Solutions Repository

This repository contains my solutions to LeetCode problems implemented in Python. Problems are categorized by topic to track progress and improve algorithmic thinking for coding interviews and competitive programming.

Key Focus Areas:

• Problem Solving
• Data Structures
• Algorithms
• Interview Preparation
• Optimization Techniques

LeetCode Topics

Hash Table

0003-longest-substring-without-repeating-characters
0012-integer-to-roman
0017-letter-combinations-of-a-phone-number
0030-substring-with-concatenation-of-all-words
0036-valid-sudoku
0037-sudoku-solver
0208-implement-trie-prefix-tree
0264-ugly-number-ii
1189-maximum-number-of-balloons
1207-unique-number-of-occurrences
1331-rank-transform-of-an-array
1358-number-of-substrings-containing-all-three-characters
1657-determine-if-two-strings-are-close
1679-max-number-of-k-sum-pairs
2215-find-the-difference-of-two-arrays
2352-equal-row-and-column-pairs
3016-minimum-number-of-pushes-to-type-word-ii
3020-find-the-maximum-number-of-elements-in-subset
3312-sorted-gcd-pair-queries
3518-smallest-palindromic-rearrangement-ii
3532-path-existence-queries-in-a-graph-i
3737-count-subarrays-with-majority-element-i
3739-count-subarrays-with-majority-element-ii

String

0003-longest-substring-without-repeating-characters
0005-longest-palindromic-substring
0008-string-to-integer-atoi
0010-regular-expression-matching
0012-integer-to-roman
0017-letter-combinations-of-a-phone-number
0022-generate-parentheses
0028-find-the-index-of-the-first-occurrence-in-a-string
0030-substring-with-concatenation-of-all-words
0067-add-binary
0087-scramble-string
0091-decode-ways
0093-restore-ip-addresses
0097-interleaving-string
0151-reverse-words-in-a-string
0208-implement-trie-prefix-tree
0392-is-subsequence
0394-decode-string
0443-string-compression
0649-dota2-senate
1071-greatest-common-divisor-of-strings
1081-smallest-subsequence-of-distinct-characters
1189-maximum-number-of-balloons
1358-number-of-substrings-containing-all-three-characters
1456-maximum-number-of-vowels-in-a-substring-of-given-length
1657-determine-if-two-strings-are-close
1768-merge-strings-alternately
1967-number-of-strings-that-appear-as-substrings-in-word
2390-removing-stars-from-a-string
3014-minimum-number-of-pushes-to-type-word-i
3016-minimum-number-of-pushes-to-type-word-ii
3499-maximize-active-section-with-trade-i
3501-maximize-active-section-with-trade-ii
3517-smallest-palindromic-rearrangement-i
3518-smallest-palindromic-rearrangement-ii
3756-concatenate-non-zero-digits-and-multiply-by-sum-ii

Sliding Window

0003-longest-substring-without-repeating-characters
0030-substring-with-concatenation-of-all-words
0643-maximum-average-subarray-i
1004-max-consecutive-ones-iii
1358-number-of-substrings-containing-all-three-characters
1456-maximum-number-of-vowels-in-a-substring-of-given-length
1493-longest-subarray-of-1s-after-deleting-one-element

Math

0009-palindrome-number
0012-integer-to-roman
0029-divide-two-integers
0050-powx-n
0062-unique-paths
0067-add-binary
0263-ugly-number
0264-ugly-number-ii
0628-maximum-product-of-three-numbers
1071-greatest-common-divisor-of-strings
1344-angle-between-hands-of-a-clock
1840-maximum-building-height
1979-find-greatest-common-divisor-of-array
3014-minimum-number-of-pushes-to-type-word-i
3312-sorted-gcd-pair-queries
3336-find-the-number-of-subsequences-with-equal-gcd
3514-number-of-unique-xor-triplets-ii
3518-smallest-palindromic-rearrangement-ii
3536-maximum-product-of-two-digits
3700-number-of-zigzag-arrays-ii
3754-concatenate-non-zero-digits-and-multiply-by-sum-i
3756-concatenate-non-zero-digits-and-multiply-by-sum-ii
3867-sum-of-gcd-of-formed-pairs

Array

0004-median-of-two-sorted-arrays
0011-container-with-most-water
0015-3sum
0016-3sum-closest
0018-4sum
0026-remove-duplicates-from-sorted-array
0027-remove-element
0031-next-permutation
0036-valid-sudoku
0037-sudoku-solver
0045-jump-game-ii
0051-n-queens
0055-jump-game
0063-unique-paths-ii
0074-search-a-2d-matrix
0136-single-number
0216-combination-sum-iii
0238-product-of-array-except-self
0283-move-zeroes
0334-increasing-triplet-subsequence
0605-can-place-flowers
0628-maximum-product-of-three-numbers
0643-maximum-average-subarray-i
0724-find-pivot-index
0735-asteroid-collision
0739-daily-temperatures
0994-rotting-oranges
1004-max-consecutive-ones-iii
1207-unique-number-of-occurrences
1260-shift-2d-grid
1288-remove-covered-intervals
1301-number-of-paths-with-max-score
1331-rank-transform-of-an-array
1431-kids-with-the-greatest-number-of-candies
1493-longest-subarray-of-1s-after-deleting-one-element
1679-max-number-of-k-sum-pairs
1732-find-the-highest-altitude
1833-maximum-ice-cream-bars
1840-maximum-building-height
1846-maximum-element-after-decreasing-and-rearranging
1926-nearest-exit-from-entrance-in-maze
1967-number-of-strings-that-appear-as-substrings-in-word
1979-find-greatest-common-divisor-of-array
2215-find-the-difference-of-two-arrays
2352-equal-row-and-column-pairs
2812-find-the-safest-path-in-a-grid
3020-find-the-maximum-number-of-elements-in-subset
3286-find-a-safe-walk-through-a-grid
3312-sorted-gcd-pair-queries
3336-find-the-number-of-subsequences-with-equal-gcd
3501-maximize-active-section-with-trade-ii
3514-number-of-unique-xor-triplets-ii
3532-path-existence-queries-in-a-graph-i
3534-path-existence-queries-in-a-graph-ii
3620-network-recovery-pathways
3737-count-subarrays-with-majority-element-i
3739-count-subarrays-with-majority-element-ii
3867-sum-of-gcd-of-formed-pairs

Prefix Sum

0238-product-of-array-except-self
0724-find-pivot-index
1004-max-consecutive-ones-iii
1732-find-the-highest-altitude
3312-sorted-gcd-pair-queries
3737-count-subarrays-with-majority-element-i
3739-count-subarrays-with-majority-element-ii
3756-concatenate-non-zero-digits-and-multiply-by-sum-ii

Sorting

0015-3sum
0016-3sum-closest
0018-4sum
0628-maximum-product-of-three-numbers
1288-remove-covered-intervals
1331-rank-transform-of-an-array
1657-determine-if-two-strings-are-close
1679-max-number-of-k-sum-pairs
1833-maximum-ice-cream-bars
1840-maximum-building-height
1846-maximum-element-after-decreasing-and-rearranging
3016-minimum-number-of-pushes-to-type-word-ii
3517-smallest-palindromic-rearrangement-i
3534-path-existence-queries-in-a-graph-ii
3536-maximum-product-of-two-digits
3867-sum-of-gcd-of-formed-pairs

Greedy

0011-container-with-most-water
0045-jump-game-ii
0055-jump-game
0334-increasing-triplet-subsequence
0605-can-place-flowers
0649-dota2-senate
1081-smallest-subsequence-of-distinct-characters
1833-maximum-ice-cream-bars
1846-maximum-element-after-decreasing-and-rearranging
3014-minimum-number-of-pushes-to-type-word-i
3016-minimum-number-of-pushes-to-type-word-ii
3534-path-existence-queries-in-a-graph-ii

Counting Sort

1189-maximum-number-of-balloons
1657-determine-if-two-strings-are-close
1833-maximum-ice-cream-bars
3016-minimum-number-of-pushes-to-type-word-ii
3312-sorted-gcd-pair-queries
3517-smallest-palindromic-rearrangement-i
3518-smallest-palindromic-rearrangement-ii
3737-count-subarrays-with-majority-element-i

Two Pointers

0005-longest-palindromic-substring
0011-container-with-most-water
0015-3sum
0016-3sum-closest
0018-4sum
0026-remove-duplicates-from-sorted-array
0027-remove-element
0028-find-the-index-of-the-first-occurrence-in-a-string
0031-next-permutation
0151-reverse-words-in-a-string
0283-move-zeroes
0392-is-subsequence
0443-string-compression
1679-max-number-of-k-sum-pairs
1768-merge-strings-alternately
2095-delete-the-middle-node-of-a-linked-list
3534-path-existence-queries-in-a-graph-ii
3867-sum-of-gcd-of-formed-pairs

Dynamic Programming

0005-longest-palindromic-substring
0010-regular-expression-matching
0022-generate-parentheses
0045-jump-game-ii
0055-jump-game
0062-unique-paths
0063-unique-paths-ii
0087-scramble-string
0091-decode-ways
0095-unique-binary-search-trees-ii
0097-interleaving-string
0264-ugly-number-ii
0338-counting-bits
0392-is-subsequence
1301-number-of-paths-with-max-score
1372-longest-zigzag-path-in-a-binary-tree
1493-longest-subarray-of-1s-after-deleting-one-element
3336-find-the-number-of-subsequences-with-equal-gcd
3534-path-existence-queries-in-a-graph-ii
3620-network-recovery-pathways
3700-number-of-zigzag-arrays-ii

Divide and Conquer

0004-median-of-two-sorted-arrays
0023-merge-k-sorted-lists
3737-count-subarrays-with-majority-element-i
3739-count-subarrays-with-majority-element-ii

Segment Tree

3501-maximize-active-section-with-trade-ii
3737-count-subarrays-with-majority-element-i
3739-count-subarrays-with-majority-element-ii

Merge Sort

0023-merge-k-sorted-lists
3737-count-subarrays-with-majority-element-i
3739-count-subarrays-with-majority-element-ii

Binary Search

0004-median-of-two-sorted-arrays
0074-search-a-2d-matrix
1004-max-consecutive-ones-iii
2812-find-the-safest-path-in-a-grid
3312-sorted-gcd-pair-queries
3501-maximize-active-section-with-trade-ii
3532-path-existence-queries-in-a-graph-i
3534-path-existence-queries-in-a-graph-ii
3620-network-recovery-pathways

Tree

0095-unique-binary-search-trees-ii
0099-recover-binary-search-tree
0101-symmetric-tree
0104-maximum-depth-of-binary-tree
0199-binary-tree-right-side-view
0236-lowest-common-ancestor-of-a-binary-tree
0437-path-sum-iii
0872-leaf-similar-trees
1161-maximum-level-sum-of-a-binary-tree
1372-longest-zigzag-path-in-a-binary-tree
1448-count-good-nodes-in-binary-tree

Depth-First Search

0099-recover-binary-search-tree
0101-symmetric-tree
0104-maximum-depth-of-binary-tree
0199-binary-tree-right-side-view
0236-lowest-common-ancestor-of-a-binary-tree
0437-path-sum-iii
0872-leaf-similar-trees
1161-maximum-level-sum-of-a-binary-tree
1372-longest-zigzag-path-in-a-binary-tree
1448-count-good-nodes-in-binary-tree
2492-minimum-score-of-a-path-between-two-cities
2685-count-the-number-of-complete-components

Breadth-First Search

0101-symmetric-tree
0104-maximum-depth-of-binary-tree
0199-binary-tree-right-side-view
0994-rotting-oranges
1161-maximum-level-sum-of-a-binary-tree
1448-count-good-nodes-in-binary-tree
1926-nearest-exit-from-entrance-in-maze
2492-minimum-score-of-a-path-between-two-cities
2685-count-the-number-of-complete-components
2812-find-the-safest-path-in-a-grid
3286-find-a-safe-walk-through-a-grid

Binary Tree

0095-unique-binary-search-trees-ii
0099-recover-binary-search-tree
0101-symmetric-tree
0104-maximum-depth-of-binary-tree
0199-binary-tree-right-side-view
0236-lowest-common-ancestor-of-a-binary-tree
0437-path-sum-iii
0872-leaf-similar-trees
1161-maximum-level-sum-of-a-binary-tree
1372-longest-zigzag-path-in-a-binary-tree
1448-count-good-nodes-in-binary-tree

Backtracking

0017-letter-combinations-of-a-phone-number
0022-generate-parentheses
0037-sudoku-solver
0051-n-queens
0052-n-queens-ii
0093-restore-ip-addresses
0095-unique-binary-search-trees-ii
0216-combination-sum-iii

Recursion

0010-regular-expression-matching
0021-merge-two-sorted-lists
0024-swap-nodes-in-pairs
0025-reverse-nodes-in-k-group
0050-powx-n
0394-decode-string

Linked List

0021-merge-two-sorted-lists
0023-merge-k-sorted-lists
0024-swap-nodes-in-pairs
0025-reverse-nodes-in-k-group
0328-odd-even-linked-list
2095-delete-the-middle-node-of-a-linked-list

Enumeration

1291-sequential-digits
3020-find-the-maximum-number-of-elements-in-subset
3499-maximize-active-section-with-trade-i
3514-number-of-unique-xor-triplets-ii

Bit Manipulation

0029-divide-two-integers
0067-add-binary
0136-single-number
0338-counting-bits
0693-binary-number-with-alternating-bits
1318-minimum-flips-to-make-a-or-b-equal-to-c
3514-number-of-unique-xor-triplets-ii
3534-path-existence-queries-in-a-graph-ii

Heap (Priority Queue)

0023-merge-k-sorted-lists
0264-ugly-number-ii
2812-find-the-safest-path-in-a-grid
3286-find-a-safe-walk-through-a-grid
3620-network-recovery-pathways

Combinatorics

0062-unique-paths
3312-sorted-gcd-pair-queries
3518-smallest-palindromic-rearrangement-ii

Binary Search Tree

0095-unique-binary-search-trees-ii
0099-recover-binary-search-tree

Union-Find

2492-minimum-score-of-a-path-between-two-cities
2685-count-the-number-of-complete-components
2812-find-the-safest-path-in-a-grid
3532-path-existence-queries-in-a-graph-i

Matrix

0036-valid-sudoku
0037-sudoku-solver
0063-unique-paths-ii
0074-search-a-2d-matrix
0994-rotting-oranges
1260-shift-2d-grid
1301-number-of-paths-with-max-score
1926-nearest-exit-from-entrance-in-maze
2352-equal-row-and-column-pairs
2812-find-the-safest-path-in-a-grid
3286-find-a-safe-walk-through-a-grid

String Matching

0028-find-the-index-of-the-first-occurrence-in-a-string

Graph Theory

2492-minimum-score-of-a-path-between-two-cities
2685-count-the-number-of-complete-components
3286-find-a-safe-walk-through-a-grid
3532-path-existence-queries-in-a-graph-i
3534-path-existence-queries-in-a-graph-ii
3620-network-recovery-pathways

Shortest Path

3286-find-a-safe-walk-through-a-grid
3620-network-recovery-pathways

Topological Sort

3620-network-recovery-pathways

Concurrency

1114-print-in-order

Simulation

0067-add-binary
0735-asteroid-collision
1260-shift-2d-grid
2352-equal-row-and-column-pairs
2390-removing-stars-from-a-string
3867-sum-of-gcd-of-formed-pairs

Database

0176-second-highest-salary
0180-consecutive-numbers
0182-duplicate-emails
0185-department-top-three-salaries
0196-delete-duplicate-emails
0197-rising-temperature
0550-game-play-analysis-iv
0570-managers-with-at-least-5-direct-reports
0577-employee-bonus
0584-find-customer-referee
0585-investments-in-2016
0595-big-countries
0596-classes-with-at-least-5-students
0602-friend-requests-ii-who-has-the-most-friends
0610-triangle-judgement
0619-biggest-single-number
0620-not-boring-movies
0626-exchange-seats
1045-customers-who-bought-all-products
1068-product-sales-analysis-i
1070-product-sales-analysis-iii
1075-project-employees-i
1141-user-activity-for-the-past-30-days-i
1148-article-views-i
1164-product-price-at-a-given-date
1174-immediate-food-delivery-ii
1193-monthly-transactions-i
1204-last-person-to-fit-in-the-bus
1211-queries-quality-and-percentage
1251-average-selling-price
1280-students-and-examinations
1321-restaurant-growth
1327-list-the-products-ordered-in-a-period
1341-movie-rating
1378-replace-employee-id-with-the-unique-identifier
1484-group-sold-products-by-the-date
1517-find-users-with-valid-e-mails
1527-patients-with-a-condition
1581-customer-who-visited-but-did-not-make-any-transactions
1633-percentage-of-users-attended-a-contest
1661-average-time-of-process-per-machine
1667-fix-names-in-a-table
1683-invalid-tweets
1729-find-followers-count
1731-the-number-of-employees-which-report-to-each-employee
1757-recyclable-and-low-fat-products
1789-primary-department-for-each-employee
1907-count-salary-categories
1934-confirmation-rate
1978-employees-whose-manager-left-the-company
2356-number-of-unique-subjects-taught-by-each-teacher

Number Theory

1979-find-greatest-common-divisor-of-array
3312-sorted-gcd-pair-queries
3336-find-the-number-of-subsequences-with-equal-gcd
3867-sum-of-gcd-of-formed-pairs

Design

0208-implement-trie-prefix-tree
0901-online-stock-span
0933-number-of-recent-calls

Queue

0649-dota2-senate
0933-number-of-recent-calls

Data Stream

0901-online-stock-span
0933-number-of-recent-calls

Stack

0394-decode-string
0735-asteroid-collision
0739-daily-temperatures
0901-online-stock-span
1081-smallest-subsequence-of-distinct-characters
2390-removing-stars-from-a-string

Monotonic Stack

0739-daily-temperatures
0901-online-stock-span
1081-smallest-subsequence-of-distinct-characters

Trie

0208-implement-trie-prefix-tree