@@ -7,110 +7,181 @@ Look here is a ladder for you. You can play it in [leetcode](https://leetcode.co
77
88Please read and follow the steps in [ CONTRIBUTING.md] ( /CONTRIBUTING.md ) .
99
10- ## 1. Defeat the Algorithm Interview
10+ #Problems by the frequency with tags.
1111
12- ### Requried
12+ ##1. String
1313
14- | # | Title | Solution | Difficulty |
15- | ---- | ------------------------------------------------------------ | -------- | ---------- |
16- | 3 | [ Longest Substring Without Repeating Characters] ( https://leetcode.com/problems/longest-substring-without-repeating-characters ) | | Medium |
17- | 5 | [ Longest Palindromic Substring] ( https://leetcode.com/problems/longest-palindromic-substring ) | | Medium |
18- | 125 | [ Valid Palindrome] ( https://leetcode.com/problems/valid-palindrome/ ) | | Easy |
19- | 14 | [ Longest Common Prefix] ( https://leetcode.com/problems/longest-common-prefix ) | | Easy |
20- | 8 | [ String to Integer (atoi)] ( https://leetcode.com/problems/string-to-integer-atoi ) | | Medium |
14+ | # Title |
15+ | ------------------------------------------------------------ |
16+ | [ 423. Reconstruct Original Digits from English] ( https://leetcode.com/problems/reconstruct-original-digits-from-english ) |
17+ | [ 1249. Minimum Remove to Make Valid Parentheses] ( https://leetcode.com/problems/minimum-remove-to-make-valid-parentheses ) |
18+ | [ 20. Valid Parentheses] ( https://leetcode.com/problems/valid-parentheses ) |
19+ | [ 3. Longest Substring Without Repeating Characters] ( https://leetcode.com/problems/longest-substring-without-repeating-characters ) |
20+ | [ 68. Text Justification] ( https://leetcode.com/problems/text-justification ) |
21+ | [ 811. Subdomain Visit Count] ( https://leetcode.com/problems/subdomain-visit-count ) |
22+ | [ 680. Valid Palindrome II] ( https://leetcode.com/problems/valid-palindrome-ii ) |
23+ | [ 5. Longest Palindromic Substring] ( https://leetcode.com/problems/longest-palindromic-substring ) |
2124
22- ### Optional
2325
24- | # | Title | Solution | Difficulty |
25- | ---- | ------------------------------------------------------------ | -------- | ---------- |
26- | 344 | [ Reverse String] ( https://leetcode.com/problems/reverse-string ) | | Easy |
27- | 13 | [ Roman to Integer] ( https://leetcode.com/problems/roman-to-integer ) | | Easy |
28- | 10 | [ Regular Expression Matching] ( https://leetcode.com/problems/regular-expression-matching ) | | Hard |
2926
27+ ## 2. Breadth-First Search
3028
29+ | # Title |
30+ | ---- |
31+ | [ 200. Number of Islands] ( https://leetcode.com/problems/number-of-islands ) |
32+ | [ 815. Bus Routes] ( https://leetcode.com/problems/bus-routes ) |
33+ | [ 127. Word Ladder] ( https://leetcode.com/problems/word-ladder ) |
34+ | [ 210. Course Schedule II] ( https://leetcode.com/problems/course-schedule-ii ) |
35+ | [ 529. Minesweeper] ( https://leetcode.com/problems/minesweeper ) |
36+ | [ 297. Serialize and Deserialize Binary Tree] ( https://leetcode.com/problems/serialize-and-deserialize-binary-tree ) |
37+ | [ 199. Binary Tree Right Side View] ( https://leetcode.com/problems/binary-tree-right-side-view ) |
38+ | [ 863. All Nodes Distance K in Binary Tree] ( https://leetcode.com/problems/all-nodes-distance-k-in-binary-tree ) |
39+ | [ 322. Coin Change] ( https://leetcode.com/problems/coin-change ) |
3140
32- ## 2. Breadth First Search
33- 34- ### Requried
35- 36- | # | Title | Solution | Difficulty |
37- | ---- | :----------------------------------------------------------- | -------- | ---------- |
38- | 200 | [ Number of Islands] ( https://leetcode.com/problems/number-of-islands ) | | Medium |
39- | 102 | [ Binary Tree Level Order Traversal] ( https://leetcode.com/problems/binary-tree-level-order-traversal/ ) | | Medium || |
40- | 127 | [ Word Ladder] ( https://leetcode.com/problems/word-ladder/ ) | | Medium |
41- | 207 | [ Course Schedule] ( https://leetcode.com/problems/course-schedule/ ) | | Medium |
42- | 210 | [ Course Schedule II] ( https://leetcode.com/problems/course-schedule-ii/ ) | | Medium |
43- | 133 | [ Clone Graph] ( https://leetcode.com/problems/clone-graph/ ) | | Medium |
44- | 297 | [ Serialize and Deserialize Binary Tree] ( https://leetcode.com/problems/serialize-and-deserialize-binary-tree/ ) | | Hard |
4541
4642
4743## 3. Binary Search
4844
49- ### Required
50- 51- | # | Title | Solution | Difficultty |
52- | ---- | -------- | -------- | ----------- |
53- | 658 | [ Find K Closest Elements] ( https://leetcode.com/problems/find-k-closest-elements ) | | Medium |
54- | 33 | [ Search in Rotated Sorted Array] ( https://leetcode.com/problems/search-in-rotated-sorted-array ) | | Medium |
55- | 50 | [ Pow(x, n)] ( https://leetcode.com/problems/powx-n ) | | Medium |
56- | 4 | [ Median of Two Sorted Arrays] ( https://leetcode.com/problems/median-of-two-sorted-arrays ) | | Hard |
57- | 29 | [ Divide Two Integers] ( https://leetcode.com/problems/divide-two-integers ) | | Medium |
58- | 315 | [ Count of Smaller Numbers After Self] ( https://leetcode.com/problems/count-of-smaller-numbers-after-self ) | | Hard |
59- | 287 | [ Find the Duplicate Number] ( https://leetcode.com/problems/find-the-duplicate-number ) | | Medium |
60- | 167 | [ Two Sum II - Input array is sorted] ( https://leetcode.com/problems/two-sum-ii-input-array-is-sorted ) | | Easy |
61- | 658 | [ Find K Closest Elements] ( https://leetcode.com/problems/find-k-closest-elements ) | | Medium |
62- 63- ### Optional
64- 65- | # | Title | Solution | Difficulty |
66- | :--- | :----------------------------------------------------------- | :------- | :--------- |
67- | 74 | [ Search a 2D Matrix] ( https://leetcode.com/problems/search-a-2d-matrix ) | | Easy |
68- | 35 | [ Search Insert Position] ( https://leetcode.com/problems/search-insert-position ) | | Easy |
69- | 278 | [ First Bad Version] ( https://leetcode.com/problems/first-bad-version ) | | Easy |
70- | 222 | [ Count Complete Tree Nodes] ( https://leetcode.com/problems/count-complete-tree-nodes ) | | Medium |
71- | 69 | [ Sqrt(x)] ( https://leetcode.com/problems/sqrtx ) | | Easy | Microsoft |
72- | 1111 | [ Maximum Nesting Depth of Two Valid Parentheses Strings] ( https://leetcode.com/problems/maximum-nesting-depth-of-two-valid-parentheses-strings ) | | Medium |
73- | 300 | [ Longest Increasing Subsequence] ( https://leetcode.com/problems/longest-increasing-subsequence ) | | Medium |
74- | 327 | [ Count of Range Sum] ( https://leetcode.com/problems/count-of-range-sum ) | | Hard |
75- | 363 | [ Max Sum of Rectangle No Larger Than K] ( https://leetcode.com/problems/max-sum-of-rectangle-no-larger-than-k ) | | Hard |
76- 77- ## 4. Binary Tree & Divide and Conquer
78- 79- ### Required
80- 81- | # | Title | Solution | Difficultty |
82- | ---- | ------------------------------------------------------------ | -------- | ----------- |
83- | 104 | [ Maximum Depth of Binary Tree] ( https://leetcode.com/problems/maximum-depth-of-binary-tree ) | | Easy |
84- | 226 | [ Invert Binary Tree] ( https://leetcode.com/problems/invert-binary-tree ) | | Easy |
85- | 617 | [ Merge Two Binary Trees] ( https://leetcode.com/problems/merge-two-binary-trees ) | | Easy |
86- | 96 | [ Unique Binary Search Trees] ( https://leetcode.com/problems/unique-binary-search-trees ) | | Medium |
87- | 173 | [ Binary Search Tree Iterator] ( https://leetcode.com/problems/binary-search-tree-iterator ) | | Medium |
88- | 169 | [ Majority Element] ( https://leetcode.com/problems/majority-element ) | | Easy |
89- | 297 | [ Serialize and Deserialize Binary Tree] ( https://leetcode.com/problems/serialize-and-deserialize-binary-tree ) | | Hard |
90- | 53 | [ Maximum Subarray] ( https://leetcode.com/problems/maximum-subarray ) | | Easy |
91- | 215 | [ Kth Largest Element in an Array] ( https://leetcode.com/problems/kth-largest-element-in-an-array ) | | Medium |
92- 93- ### Optional
94- 95- ## 5. Two Pointers
96- 97- ### Required
45+ | # Title |
46+ | ---- |
47+ | [ 4. Median of Two Sorted Arrays] ( https://leetcode.com/problems/median-of-two-sorted-arrays ) |
48+ | [ 1235. Maximum Profit in Job Scheduling] ( https://leetcode.com/problems/maximum-profit-in-job-scheduling ) |
49+ | [ 528. Random Pick with Weight] ( https://leetcode.com/problems/random-pick-with-weight ) |
50+ | [ 33. Search in Rotated Sorted Array] ( https://leetcode.com/problems/search-in-rotated-sorted-array ) |
51+ | [ 162. Find Peak Element] ( https://leetcode.com/problems/find-peak-element ) |
52+ | [ 981. Time Based Key-Value Store] ( https://leetcode.com/problems/time-based-key-value-store ) |
53+ | [ 540. Single Element in a Sorted Array] ( https://leetcode.com/problems/single-element-in-a-sorted-array ) |
54+ | [ 34. Find First and Last Position of Elemen] ( https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array ) |
55+ | [ 718. Maximum Length of Repeated Subarray] ( https://leetcode.com/problems/maximum-length-of-repeated-subarray ) |
56+ | [ 1044. Longest Duplicate Substring] ( https://leetcode.com/problems/longest-duplicate-substring ) |
57+ | [ 862. Shortest Subarray with Sum at Leas] ( https://leetcode.com/problems/shortest-subarray-with-sum-at-least-k ) |
58+ | [ 410. Split Array Largest Sum] ( https://leetcode.com/problems/split-array-largest-sum ) |
59+ | [ 74. Search a 2D Matrix] ( https://leetcode.com/problems/search-a-2d-matrix ) |
60+ | [ 287. Find the Duplicate Number] ( https://leetcode.com/problems/find-the-duplicate-number ) |
61+ 62+ 63+ 64+ ## 4. Divide and Conquer
65+ 66+ | # Title |
67+ | ---- |
68+ | [ 53. Maximum Subarray] ( https://leetcode.com/problems/maximum-subarray ) |
69+ | [ 973. K Closest Points to Origin] ( https://leetcode.com/problems/k-closest-points-to-origin ) |
70+ | [ 215. Kth Largest Element in an Array] ( https://leetcode.com/problems/kth-largest-element-in-an-array ) |
71+ | [ 23. Merge k Sorted Lists] ( https://leetcode.com/problems/merge-k-sorted-lists ) |
72+ | [ 347. Top K Frequent Elements] ( https://leetcode.com/problems/top-k-frequent-elements ) |
73+ | [ 493. Reverse Pairs] ( https://leetcode.com/problems/reverse-pairs ) |
74+ | [ 427. Construct Quad Tree] ( https://leetcode.com/problems/construct-quad-tree ) |
75+ | [ 169. Majority Element] ( https://leetcode.com/problems/majority-element ) |
76+ | [ 315. Count of Smaller Numbers After Sel] ( https://leetcode.com/problems/count-of-smaller-numbers-after-self ) |
77+ | [ 240. Search a 2D Matrix II] ( https://leetcode.com/problems/search-a-2d-matrix-ii ) |
78+ | [ 912. Sort an Array] ( https://leetcode.com/problems/sort-an-array ) |
9879
99- ## 6 . Implicit Graph DFS
10080
101- ### Required
10281
103- ## 7 . Hash & Heap
104- 105- ### Required
106- 107- ## 8 . Memoization Search & Dynamic Programming
108- 109- ### Required
110- 111- ## 9 . 4 Key Points of DP and Coordinate DP
82+ ## 5. Two Pointers
11283
113- ### Required
84+ | # Title |
85+ | ------------------------------------------------------------ |
86+ | [ 42. Trapping Rain Water] ( https://leetcode.com/problems/trapping-rain-water ) |
87+ | [ 31. Next Permutation] ( https://leetcode.com/problems/next-permutation ) |
88+ | [ 680. Valid Palindrome II] ( https://leetcode.com/problems/valid-palindrome-ii ) |
89+ | [ 15. 3Sum] ( https://leetcode.com/problems/3sum ) |
90+ | [ 809. Expressive Words] ( https://leetcode.com/problems/expressive-words ) |
91+ | [ 696. Count Binary Substrings] ( https://leetcode.com/problems/count-binary-substrings ) |
92+ | [ 11. Container With Most Water] ( https://leetcode.com/problems/container-with-most-water ) |
93+ | [ 443. String Compression] ( https://leetcode.com/problems/string-compression ) |
94+ | [ 88. Merge Sorted Array] ( https://leetcode.com/problems/merge-sorted-array ) |
95+ | [ 125. Valid Palindrome] ( https://leetcode.com/problems/valid-palindrome ) |
96+ | [ 18. 4Sum] ( https://leetcode.com/problems/4sum ) |
97+ | [ 16. 3Sum Closest] ( https://leetcode.com/problems/3sum-closest ) |
98+ | [ 151. Reverse Words in a String] ( https://leetcode.com/problems/reverse-words-in-a-string ) |
99+ 100+ 101+ 102+ ## 6. Depth-First Search
103+ 104+ | # Title |
105+ | ------------------------------------------------------------ |
106+ | [ 200. Number of Islands] ( https://leetcode.com/problems/number-of-islands ) |
107+ | [ 236. Lowest Common Ancestor of a Binary] ( https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree ) |
108+ | [ 938. Range Sum of BST] ( https://leetcode.com/problems/range-sum-of-bst ) |
109+ | [ 210. Course Schedule II] ( https://leetcode.com/problems/course-schedule-ii ) |
110+ | [ 529. Minesweeper] ( https://leetcode.com/problems/minesweeper ) |
111+ | [ 124. Binary Tree Maximum Path Sum] ( https://leetcode.com/problems/binary-tree-maximum-path-sum ) |
112+ | [ 297. Serialize and Deserialize Binary Tree] ( https://leetcode.com/problems/serialize-and-deserialize-binary-tree ) |
113+ | [ 199. Binary Tree Right Side View] ( https://leetcode.com/problems/binary-tree-right-side-view ) |
114+ | [ 987. Vertical Order Traversal of a Binary Tr] ( https://leetcode.com/problems/vertical-order-traversal-of-a-binary-tree ) |
115+ | [ 863. All Nodes Distance K in Binary Tree] ( https://leetcode.com/problems/all-nodes-distance-k-in-binary-tree ) |
116+ | [ 332. Reconstruct Itinerary] ( https://leetcode.com/problems/reconstruct-itinerary ) |
117+ | [ 695. Max Area of Island] ( https://leetcode.com/problems/max-area-of-island ) |
118+ | [ 207. Course Schedule] ( https://leetcode.com/problems/course-schedule ) |
119+ 120+ 121+ 122+ ## 7. Hash Table
123+ 124+ | # Title |
125+ | ------------------------------------------------------------ |
126+ | [ 1. Two Sum] ( https://leetcode.com/problems/two-sum ) |
127+ | [ 146. LRU Cache] ( https://leetcode.com/problems/lru-cache ) |
128+ | [ 3. Longest Substring Without Repeating] ( https://leetcode.com/problems/longest-substring-without-repeating-characters ) |
129+ | [ 560. Subarray Sum Equals K] ( https://leetcode.com/problems/subarray-sum-equals-k ) |
130+ | [ 815. Bus Routes] ( https://leetcode.com/problems/bus-routes ) |
131+ | [ 811. Subdomain Visit Count] ( https://leetcode.com/problems/subdomain-visit-count ) |
132+ | [ 380. Insert Delete GetRandom O(1)] ( https://leetcode.com/problems/insert-delete-getrandom-o1 ) |
133+ | [ 41. First Missing Positive] ( https://leetcode.com/problems/first-missing-positive ) |
134+ | [ 49. Group Anagrams] ( https://leetcode.com/problems/group-anagrams ) |
135+ 136+ ## 8. Heap(Priority Queue)
137+ 138+ | # Title |
139+ | ------------------------------------------------------------ |
140+ | [ 973. K Closest Points to Origin] ( https://leetcode.com/problems/k-closest-points-to-origin ) |
141+ | [ 215. Kth Largest Element in an Array] ( https://leetcode.com/problems/kth-largest-element-in-an-array ) |
142+ | [ 239. Sliding Window Maximum] ( https://leetcode.com/problems/sliding-window-maximum ) |
143+ | [ 347. Top K Frequent Elements] ( https://leetcode.com/problems/top-k-frequent-elements ) |
144+ | [ 295. Find Median from Data Stream] ( https://leetcode.com/problems/find-median-from-data-stream ) |
145+ | [ 692. Top K Frequent Words] ( https://leetcode.com/problems/top-k-frequent-words ) |
146+ | [ 23. Merge k Sorted Lists] ( https://leetcode.com/problems/merge-k-sorted-lists ) |
147+ | [ 621. Task Scheduler] ( https://leetcode.com/problems/task-scheduler ) |
148+ | [ 1353. Maximum Number of Events That ] ( https://leetcode.com/problems/maximum-number-of-events-that-can-be-attended ) |
149+ 150+ 151+ 152+ ## 9. Dynamic Programming
153+ 154+ | #Title |
155+ | ------------------------------------------------------------ |
156+ | [ 42. Trapping Rain Water] ( https://leetcode.com/problems/trapping-rain-water ) |
157+ | [ 53. Maximum Subarray] ( https://leetcode.com/problems/maximum-subarray ) |
158+ | [ 5. Longest Palindromic Substring] ( https://leetcode.com/problems/longest-palindromic-substring ) |
159+ | [ 121. Best Time to Buy and Sell Stock] ( https://leetcode.com/problems/best-time-to-buy-and-sell-stock ) |
160+ | [ 22. Generate Parentheses] ( https://leetcode.com/problems/generate-parentheses ) |
161+ | [ 828. Count Unique Characters of All Substrings of a Given String] ( https://leetcode.com/problems/count-unique-characters-of-all-substrings-of-a-given-string ) |
162+ | [ 1326. Minimum Number of Taps to Open to] ( https://leetcode.com/problems/minimum-number-of-taps-to-open-to-water-a-garden ) |
163+ | [ 174. Dungeon Game] ( https://leetcode.com/problems/dungeon-game ) |
164+ | [ 124. Binary Tree Maximum Path Sum] ( https://leetcode.com/problems/binary-tree-maximum-path-sum ) |
165+ | [ 871. Minimum Number of Refueling Stops] ( https://leetcode.com/problems/minimum-number-of-refueling-stops ) |
166+ | [ 10. Regular Expression Matching] ( https://leetcode.com/problems/regular-expression-matching ) |
167+ | [ 139. Word Break] ( https://leetcode.com/problems/word-break ) |
168+ | [ 140. Word Break II] ( https://leetcode.com/problems/word-break-ii ) |
169+ | [ 221. Maximal Square] ( https://leetcode.com/problems/maximal-square ) |
170+ | [ 1048. Longest String Chain] ( https://leetcode.com/problems/longest-string-chain ) |
171+ | [ 926. Flip String to Monotone Increasing] ( https://leetcode.com/problems/flip-string-to-monotone-increasing ) |
172+ | [ 45. Jump Game II] ( https://leetcode.com/problems/jump-game-ii ) |
173+ | [ 44. Wildcard Matching] ( https://leetcode.com/problems/wildcard-matching ) |
174+ | [ 198. House Robber] ( https://leetcode.com/problems/house-robber ) |
175+ 176+ ## 10. Memoization
177+ 178+ | # Title |
179+ | ------------------------------------------------------------ |
180+ | [ 139. Word Break] ( https://leetcode.com/problems/word-break ) |
181+ | [ 140. Word Break II] ( https://leetcode.com/problems/word-break-ii ) |
182+ | [ 329. Longest Increasing Path in a Matrix] ( https://leetcode.com/problems/longest-increasing-path-in-a-matrix ) |
183+ | [ 241. Different Ways to Add Parentheses] ( https://leetcode.com/problems/different-ways-to-add-parentheses ) |
184+ | [ 1611. Minimum One Bit Operations to M] ( https://leetcode.com/problems/minimum-one-bit-operations-to-make-integers-zero ) |
114185
115186## License
116187
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