My personal leetcode answers
This is a continually updated, open source project.
🎉🎉🎉 Finished 100 questions on 2018-05-28
🎉🎉🎉 Finished 150 questions on 2018-06-29
☝️Hey!!!, its clickable. references are moved💦
| Problem | Solution | Time | Difficulty | Tag | Note |
|---|---|---|---|---|---|
| 202.happy-number | cpp, python | O(N) | Easy | ||
| 836.rectangle-overlap | cpp | O(1) | Easy |
| Problem | Solution | Time | Difficulty | Tag | Note |
|---|---|---|---|---|---|
| 136.single-number | cpp | O(N) | Easy |
| Problem | Solution | Time | Difficulty | Tag | Note |
|---|---|---|---|---|---|
| 53.maximum-subarray | python | O(N) | Easy | ||
| 54.spiral-matrix | cpp | O(N) | Medium | ||
| 66.plus-one | cpp | O(N) | Easy | ||
| 118.pascals-triangle | cpp | O(N^2) | Easy | ||
| 240.search-a-2d-matrix-ii | cpp, python | O(N + M) | Medium | ||
| 350.intersection-of-two-arrays-ii | python | O(N * logN) | Easy | ||
| 485.max-consecutive-ones | cpp | O(N) | Easy | ||
| 498.diagonal-traverse | cpp | O(M * N) | Medium | ||
| 560.subarray-sum-equals-k | python | O(N) | Medium | ||
| 561.array-partition-i | cpp | O(N * logN) | Easy | ||
| 724.find-pivot-index | cpp | O(N) | Easy | ||
| 747.largest-number-at-least-twice-of-others | cpp | O(N) | Easy | ||
| 796.rotate-string | cpp, python | O(N^2) | Easy | string | TODO: Rabin-Karp Algorithm, KMP algorithm |
| 859.buddy-strings | cpp | O(N) | Easy | string |
| Problem | Solution | Time | Space | Difficulty | Tag | Note |
|---|---|---|---|---|---|---|
| 003.longest-substring-without-repeating-characters | cpp, python | O(N) | O(N) | Medium | ||
| 026.remove-duplicates-from-sorted-array | cpp, python | O(N) | O(1) | Easy | ||
| 027.remove-element | cpp, python | O(N) | O(1) | Easy | ||
| 028.implement-strstr | cpp, python | O(N^2) | O(1) | Easy | TODO: string, KMP, rolling hash? | |
| 076.minimum-window-substring | cpp, python | O(N) | O(N) | Hard | ||
| 088.merge-sorted-array | cpp, python | O(N + M) | O(1) | Easy | ||
| 125.valid-palindrome | cpp, python | O(N) | O(1) | Easy | ||
| 141.linked-list-cycle | cpp, python | O(N) | O(1) | Easy | ||
| 159.longest-substring-with-at-most-two-distinct-characters | cpp, python | O(N) | O(N) | HARD | ||
| 167.two-sum-ii-input-array-is-sorted | cpp, python | O(N) | O(1) | Easy | ||
| 209.minimum-size-subarray-sum | cpp, python | O(N) | O(1) | Medium | ||
| 234.palindrome-linked-list | cpp, python | O(N) | O(1) | Easy | maybe harder | |
| 283.move-zeroes | cpp, python | O(N) | O(1) | Easy | ||
| 340.longest-substring-with-at-most-k-distinct-characters | cpp, python | O(N) | O(N) | HARD | ||
| 344.reverse-string | cpp, python | O(N) | O(1) | Easy | ||
| 345.reverse-vowels-of-a-string | cpp, python | O(N) | O(1) | Easy | ||
| 349.intersection-of-two-arrays | cpp, python | O(K * logK), k = max(M, N) | O(1) | Easy | hash, binary-search | |
| 350.intersection-of-two-arrays-ii | cpp, python | O(K * logK), k = max(M, N) | O(1) | Easy | hash, binary-search | |
| 532.k-diff-pairs-in-an-array | cpp, python | O(N * logN) | O(1) | Easy | Hash | |
| 844.backspace-string-compare | cpp, python | O(N) | O(1) | Easy | stack |
| Problem | Solution | Time | Difficulty | Tag | Note |
|---|---|---|---|---|---|
| 15.3sum | cpp, python | O(N^2) | Medium | ||
| 16.3sum-closest | cpp, python | O(N^2) | Medium | ||
| 18.4sum | cpp, python | O(N^3) | Medium | ||
| 19.remove-nth-node-from-end-of-list | cpp, python | O(N) | Medium | ||
| 75.sort-colors | cpp python | O(N) | Medium | counting-sort | |
| 142.linked-list-cycle-ii | python | O(N) | Medium | linked-list | |
| 160.intersection-of-two-linked-lists | python | O(N + M) | Easy | linked-list |
| Problem | Solution | Time | Difficulty | Tag | Note |
|---|---|---|---|---|---|
| 21.merge-two-sorted-lists | cpp, python | O(N) | Easy | ||
| 25.reverse-nodes-in-k-group | python | O(N) | Hard | ||
| 61.rotate-list | python | O(N) | Medium | ||
| 86.partition-list | python | O(N) | Medium | ||
| 92.reverse-linked-list-ii | python | O(N) | Medium | ||
| 138.copy-list-with-random-pointer | python | O(N) | Medium | ||
| 143.reorder-list | python | O(N) | Medium | ||
| 148.sort-list | python | O(N * logN) | Medium | ||
| 203.remove-linked-list-elements | python | O(N) | Easy | ||
| 206.reverse-linked-list | python | O(N) | Easy | ||
| 237.delete-node-in-a-linked-list | python | O(1) | Easy | ||
| 328.odd-even-linked-list | python | O(N) | Medium |
| Problem | Solution | Time | Difficulty | Tag | Note |
|---|---|---|---|---|---|
| 33.search-in-rotated-sorted-array | cpp, python | O(logN) | Medium | ||
| 34.find-first-and-last-position-of-element-in-sorted-array | cpp | Medium | |||
| 74.search-a-2d-matrix | cpp, python | O(logN) | Medium | N = row * column | |
| 81.search-in-rotated-sorted-array-ii | cpp, python | O(logN) ~ O(N) | Medium | ||
| 153.find-minimum-in-rotated-sorted-array | cpp, python | O(logN) | Medium | ||
| 154.find-minimum-in-rotated-sorted-array-ii | cpp, python | O(logN) ~ O(N) | Hard | ||
| 162.find-peak-element | cpp | O(logN) | Meidum | ||
| 302.smallest-rectangle-enclosing-black-pixels | cpp | O(M * N) / O(N * LogN) | Hard |
| Problem | Solution | Time | Space | Difficulty | Tag | Note |
|---|---|---|---|---|---|---|
| 069.sqrtx | cpp, python | O(logN) | O(1) | Easy | ||
| 278.first-bad-version | cpp, python | O(logN) | O(1) | Easy | ||
| 704.binary-search | cpp, python | O(logN) | O(1) | Easy | ||
| 852.peak-index-in-a-mountain-array | cpp, python | O(logN) | O(1) | Easy | Golden-section search |
| Problem | Solution | Time | Difficulty | Tag | Note |
|---|---|---|---|---|---|
| 4.median-of-two-sorted-arrays | cpp, python | O(log(M + N)) | Hard | ||
| 98.validate-binary-search-tree | cpp, python | O(N) | Medium | TODO: inorder-traversal | |
| 104.maximum-depth-of-binary-tree | cpp, python | O(N) | Easy | ||
| 110.balanced-binary-tree | cpp, python | O(N) | Easy | ||
| 236.lowest-common-ancestor-of-a-binary-tree | cpp, python | O(N) | Medium |
| Problem | Solution | Time | Difficulty | Tag | Note |
|---|---|---|---|---|---|
| 94.binary-tree-inorder-traversal | cpp | O(N) | Medium | ||
| 102.binary-tree-level-order-traversal | cpp | O(N) | Medium | ||
| 107.binary-tree-level-order-traversal-ii | cpp | O(N) | Easy | ||
| 144.binary-tree-preorder-traversal | cpp | O(N) | Medium |
| Problem | Solution | Time | Difficulty | Tag | Note |
|---|---|---|---|---|---|
| 127.word-ladder | python | O(N * L^2) | Medium | BFS | |
| 200.number-of-islands | python | O(M x N) | Medium | BFS/DFS | union-find |
| 207.course-schedule | cpp | O(V + E) | Medium | ||
| 210.course-schedule-ii | cpp | O(V + E) | Medium | topological-sort | |
| 444.sequence-reconstruction | cpp, python | O(V+E) | Medium | topological-sort |
| Problem | Solution | Time | Difficulty | Tag | Note |
|---|---|---|---|---|---|
| 39.combination-sum | python | ??? | Medium | DFS | |
| 40.combination-sum-ii | python | ??? | Medium | DFS | |
| 46.permutations | python | ??? | Medium | DFS | |
| 47.permutations-ii | python | ??? | Medium | DFS | |
| 51.n-queens | python | ??? | Hard | DFS | |
| 52.n-queens-ii | python | ??? | Hard | DFS | |
| 78.subsets | cpp, python | O(N * 2^N) | Medium | DFS | bit-manipulation / iterative |
| 90.subsets-ii | cpp, python | O(N * 2^N) | Medium | DFS | bit-manipulation |
| 126.word-ladder-ii | python | O((V+E) * L^2) | Hard | BFS+DFS | |
| 131.palindrome-partitioning | python | ??? | Medium | DFS |
| Problem | Solution | Time | Space | Difficulty | Tag | Note |
|---|---|---|---|---|---|---|
| 079.word-search | cpp, python | O(M * N * L * L) | O(M * N) | Medium | DFS | L = length of words |
| Problem | Solution | Time | Difficulty | Tag | Note |
|---|---|---|---|---|---|
| 1.two-sum | cpp, python | O(N) | Easy | ||
| 36.valid-sudoku | cpp | O(N ^ 2) | Medium | array-indexes | |
| 49.group-anagrams | cpp | O(N * k * Logk) | Medium | ||
| 170.two-sum-iii-data-structure-design | cpp, python | O(N) | Easy | ||
| 202.happy-number | cpp, python | O(N) | Easy | ||
| 205.isomorphic-strings | cpp, python | O(N) | Easy | ||
| 217.contains-duplicate | cpp | O(N) | Easy | ||
| 219.contains-duplicate-ii | cpp | O(N) | Easy | ||
| 249.group-shifted-strings | cpp | O(N * K) | Medium | ||
| 288.unique-word-abbreviation | cpp | - | Medium | ||
| 347.top-k-frequent-elements | cpp | O(N * LogN) | Medium | TODO: quick-sort, bucket-sort | |
| 349.intersection-of-two-arrays | cpp | O(M + N) | Easy | ||
| 350.intersection-of-two-arrays-ii | cpp | O(M * N) | Easy | ||
| 359.logger-rate-limiter | cpp | O(1) | Easy | amortized | |
| 380.insert-delete-getrandom-o1 | cpp | O(1) | Medium | ||
| 454.4sum-ii | cpp | O(N ^ 2) | Medium | ||
| 599.minimum-index-sum-of-two-lists | cpp | O(M + N) | Easy | ||
| 652.find-duplicate-subtrees | cpp | O(N) | Medium | ||
| 771.jewels-and-stones | cpp | O(M + N) | Easy |
| Problem | Solution | Time | Space | Difficulty | Tag | Note |
|---|---|---|---|---|---|---|
| 23.merge-k-sorted-lists | cpp | O(N * LogK) | - | Hard | TODO: merge-sort, bottom-up | |
| 378.kth-smallest-element-in-a-sorted-matrix | cpp, python | O((K + M) * LogM) | O(M) | Medium | TODO: binary-search, O(N) solution |
| Problem | Solution | Time | Difficulty | Tag | Note |
|---|---|---|---|---|---|
| 62.unique-paths | python | O(M * N) | Medium | Coordinates | |
| 63.unique-paths-ii | python | O(M * N) | Medium | Coordinates | |
| 64.minimum-path-sum | python | O(M * N) | Medium | Coordinates | |
| 70.climbing-stairs | cpp, python | O(N) | Easy | Coordinates | |
| 91.decode-ways | cpp | O(N) | Medium | conditional-climbing-stairs | |
| 120.triangle | cpp, python | O(N^2) | Medium | Coordinates | |
| 300.longest-increasing-subsequence | cpp, python | O(N^2) | Medium | follow-up is tricky | |
| 354.russian-doll-envelopes | cpp, python | O(N^2) | Hard | TODO: Python Version Time Limit Exceeded | |
| 368.largest-divisible-subset | cpp | O(N^2) | Medium | ||
| 403.frog-jump | cpp | O(N^2) | Hard |
| Problem | Solution | Time | Difficulty | Tag | Note |
|---|---|---|---|---|---|
| 45.jump-game-ii | cpp, python | O(N) | Hard | ||
| 55.jump-game | cpp, python | O(N) | Medium | dynamic-programming |
| Problem | Solution | Time | Space | Difficulty | Tag | Note |
|---|---|---|---|---|---|---|
| 128.longest-consecutive-sequence | cpp | O(N) | - | Hard | ||
| 261.graph-valid-tree | cpp, python | O(N) | O(N) | Medium | BFS/DFS | |
| 305.number-of-islands-ii | cpp, python | O(N) | O(M * N) | Hard | N = len(positions) | |
| 721.accounts-merge | cpp, python | O(M * N) | O(M * N) | Medium |
| Problem | Solution | Time | Space | Difficulty | Tag | Note |
|---|---|---|---|---|---|---|
| 208.implement-trie-prefix-tree | cpp, python | O(L) | <= (N * L) | Medium | - | L = len(word), N = number of words |
| 211.add-and-search-word-data-structure-design | cpp, python | add = O(L), find >= O(L) | <= O(N * L) | Medium | DFS | L = len(word), N = number of words |
| 212.word-search-ii | cpp, python | O(M * N * L * L) | MAX(O(M * N), O(K * L)) | HARD | DFS | K = number of words, L = avg length of words |
| Problem | Solution | Time | Space | Difficulty | Tag | Note |
|---|---|---|---|---|---|---|
| 215.kth-largest-element-in-an-array | cpp, python | O(N) | O(1) | Medium | quick-select | best = O(N), worst = O(N^2) |
| Problem | Solution | Time | Space | Difficulty | Tag | Note |
|---|---|---|---|---|---|---|
| 465.kth-smallest-sum-in-two-sorted-arrays | cpp, python | O((K + N) * LogN) | O(N) | Hard | heap | N = B.size() |
| 543.kth-largest-in-n-arrays | cpp, python | O(M * N * LogK) | O(K) | Easy | heap | |
| 589.connecting-graph | cpp, python | O(1) | O(N) | Medium | union-find | |
| 590.connecting-graph-ii | cpp, python | O(1) | O(N) | Medium | union-find | |
| 591.connecting-graph-iii | cpp, python | O(1) | O(N) | Medium | union-find | |
| 629.minimum-spanning-tree | cpp, python | O(N * logN) | O(N) | Hard | union-find, Kruskal | Prim |