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👨‍💻 This repository contains the solutions and explanations to the algorithm problems on LintCode. All are written in Python/Java/C++ and implemented by myself.

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<h3 align="center"><strong>LintCode Online Judge</strong></h3>

![](https://files.realpython.com/media/Python-Interview-Questions_Watermarked.5c5245ea8638.jpg)

#### [Binary Search](./Binary_Search/)

457.Classical Binary Search  
14.First Position of Target  
458.Last Position of Target  
61.Search for a Range  
74.First Bad Version  
447.Search in a Big Sorted Array  
60.Search Insert Position  
28.Search a 2D Matrix  
38.Search a 2D Matrix II (M)  
462.Total Occurrence of Target  
585.Maximum Number in Mountain Sequence  
75.Find Peak Element  
141.Sqrt(x)  
586.Sqrt(x) II  
248.Count of Smaller Number (M)  
159.Find Minimum in Rotated Sorted Array  
160.Find Minimum in Rotated Sorted Array II  
62.Search in Rotated Sorted Array (M)  
460.Find K Closest Elements (k closest numbers in sorted array)  
**65.Median of two Sorted Arrays** (H)  
249.Count of Smaller Number before itself (H)  
183.Wood Cut (H)  
437.Copy Books (H)  
600.Smallest Rectangle Enclosing Black Pixels (H)  
940.Maximum Absolute Value (M)  
1626.Salary Adjustment (M)

#### [Tree](./Tree/)

> Divide and Conquer

66.Binary Tree Preorder Traversal  
67.Binary Tree Inorder Traversal  
68.Binary Tree Postorder Traversal  
97.Maximum Depth of Binary Tree  
480.Binary Tree Paths  
596.Minimum Subtree  
628.Maximum Subtree  
93.Balanced Binary Tree  
597.Subtree with Maximum Average  
453.Flatten Binary Tree to Linked List  
88.Lowest Common Ancestor of a Binary Tree (M)  
474.Lowest Common Ancestor II  
578.Lowest Common Ancestor III (M)  
595.Binary Tree Longest Consecutive Sequence  
614.Binary Tree Longest Consecutive Sequence II (M)  
619.Binary Tree Longest Consecutive Sequence III (M)  
94.Binary Tree Maximum Path Sum (M)  
376.Binary Tree Path Sum  
246.Binary Tree Path Sum II  
472.Binary Tree Path Sum III (H)  
863.Binary Tree Path Sum IV (M)  
378.Convert Binary Tree to Doubly Linked List (M)  
650.Find Leaves of Binary Tree

> **Binary Search Tree**

95.Validate Binary Search Tree (M)  
86.Binary Search Tree Iterator (H)  
448.Inorder Successor in BST (M)  
11.Search Range in Binary Search Tree (M)  
85.Insert Node in a Binary Search Tree  
87.Remove Node in Binary Search Tree (H)

#### [BFS](./BFS/)

69.Binary Tree Level Order Traversal  
7.Serialize and Deserialize Binary Tree  
71.Binary Tree Zigzag Level Order Traversal  
70.Binary Tree Level Order Traversal II  
242.Convert Binary Tree to Linked Lists by Depth  
178.Graph Valid Tree  
137.Clone Graph  
618.Search Graph Nodes  
127.Topological Sorting  
615.Course Schedule  
616.Course Schedule II  
605.Sequence Reconstruction  
433.Number of Islands  
677.Number of Big Islands  
598.Zombie in Matrix  
611.Knight Shortest Path  
573.Build Post Office II  
431.Connected Component in Undirected Graph  
120.Word Ladder (H)  
121.Word Ladder II (H)  
630.Knight Shortest Path II (M)  
1446.01 Matrix Walking Problem (M)  
375.Clone Binary Tree  
477.Surrounded Regions

#### [DFS](./DFS/)

15.Permutations (M)  
16.Permutations II (M)  
17.Subsets (M)  
18.Subsets II (M)  
152.Combinations (M)  
135.Combination Sum (M)  
153.Combination Sum II (M)    
425.Letter Combinations of a Phone Number (M)  
426.Restore IP Addresses (M)  
136.Palindrome Partitioning (M)  
121.Word Ladder II (H)  
52.Next Permutation  
190.Next Permutation II  
33.N-Queens  
790.Parser  
652.Factorization  
1353.Sum Root to Leaf Numbers  
1031.Is Graph Bipartite

#### [Linked List](./Linked_List)

450.Reverse Nodes in k-Group  
165.Merge Two Sorted Lists  
36.Reverse Linked List II  
511.Swap Two Nodes in Linked List  
98.Sort List  
99.Reorder List  
170.Rotate List  
96.Partition List  
105.Copy List with Random Pointer  
102.Linked List Cycle  
103.Linked List Cycle II (H)  
380.Intersection of Two Linked Lists  
106.Convert Sorted List to Binary Search Tree  
372.Delete Node in a Linked List

#### [Array](./Array)

41.Maximum Subarray  
604.Window Sum  
138.Subarray Sum  
139.Subarray Sum Closest  
547.Intersection of Two Arrays (3 approaches)

#### [Two Pointers](./Two_Pointers/)

100.Remove Duplicates from Sorted Array  
101.Remove Duplicates from Sorted Array II  
39.Recover Rotated Sorted Array  
64.Merge Sorted Array  
6.Merge Two Sorted Arrays (Merge Sorted Array II)  
49.Sort Letters by Case  
148.Sort Colors  
143.Sort Colors II  
144.Interleaving Positive and Negative Numbers  
373.Partition Array by Odd and Even  
415.Valid Palindrome  
461.Kth Smallest Numbers in Unsorted Array  
521.Remove Duplicate Numbers in Array  
539.Move Zeroes  
56.Two Sum  
57.3-Sum  
58.4Sum  
59.3-Sum Closest  
533.Two Sum - Closest to target
607.Two Sum III - Data structure design  
587.Two Sum - Unique pairs  
609.Two Sum - Less than or equal to target  
443.Two Sum - Greater than target  
610.Two Sum - Difference equals to target  
32.Minimum Window Substring  
384.Longest Substring Without Repeating Characters  
386.Longest Substring with At Most K Distinct Characters  
406.Minimum Size Subarray Sum  
461.Kth Smallest Numbers in Unsorted Array  
363.Trapping Rain Water  
1487.Judging Triangle

#### [Stack](./Stack/)

575.Decode String (Expression Expand)  
494.Implement Stack by Two Queues  
40.Implement Queue by Two Stacks  
224.Implement Three Stacks by Single Array (M)  
955.Implement Queue by Circular Array  
**12.Min Stack (Monotonic Stack)** (M)  
**122.Largest Rectangle in Histogram** (H)  
**510.Maximal Rectangle** (H)  
**126.Max Tree** (H)

> **Iterator 相关题**

528.Flatten Nested List Iterator  
540.Zigzag Iterator  
541.Zigzag Iterator II  
601.Flatten 2D Vector

#### [Hash](./Hash/)

129.Rehashing  
134.LRU Cache  
105.Copy List with Random Pointer  
171.Anagrams  
124.Longest Consecutive Sequence

#### [Heap](./Heap/)

104.Merge K Sorted Lists  
1272.Kth Smallest Element in a Sorted Matrix  
130.Heapify  
4.Ugly Number II  
401.Kth Smallest Number in Sorted Matrix  
465.Kth Smallest Sum In Two Sorted Arrays (H)  
471.Top K Frequent Words  
486.Merge K Sorted Arrays  
543.Kth Largest in N Arrays  
544.Top k Largest Numbers  
545.Top k Largest Numbers II  
577.Merge K Sorted Interval Lists  
612.K Closest Points  
613.High Five  
81.Find Median from Data Stream  
360.Sliding Window Median

#### [Dynamic Programming](./Dynamic_Programming/)

109.Triangle  
110.Minimum Path Sum  
114.Unique Paths  
115.Unique Paths II  
679.Unique Paths III

191.Maximum Product Subarray

> **Backpack**

0-1 背包问题

[Backpack]()  
[Backpack II]()  
[Backpack V]()  
[Backpack VI - 564.Combination Sum IV (M)]()

多重背包问题

[Backpack VII]()  
[Backpack VIII]()

完全背包问题

[Backpack III]()  
[Backpack IV]()

#### [Union Find](./Union_Find/)

433.Number of Islands  
178.Graph Valid Tree  
431.Connected Component in Undirected Graph (M)  
589.Connecting Graph (M)  
1070.Accounts Merge  
589.Connecting Graph  
590.Connecting Graph II  
591.Connecting Graph III  
434.Number of Islands II  
805.Maximum Association Set  
1396.Set Union  
1569.Social Network

#### [Trie](./Trie/)

442.Implement Trie (Prefix Tree)  
1090.Map Sum Pairs  
559.Trie Service  
132.Word Search II  
634.Word Squares

#### [Sweep Line](./Sweep_Line/)

391.Number of Airplanes in the Sky  
919.Meeting Rooms II  
821.Time Intersection

#### [Bit Manipulation](./Bit_Manipulation/)

82.Single Number  
83.Single Number II  
84.Single Number III  
824.Single Number IV

#### [String](./String/)

8.Rotate String  
53.Reverse Words in a String  
927.Reverse Words in a String II  
1173.Reverse Words in a String III  
1041.Reorganize String  
78.Longest Common Prefix  
784.The Longest Common Prefix II

#### [Sort](./Sort/)

80.Median  
5.Kth Largest Element  
894.Pancake Sorting

#### [Math](./Math/)

730.Sum of All Subsets

#### [Others](./Others/)

842.Origami  
1022.Valid Tic-Tac-Toe State

#### Resources

Below are some good resources to look through:

- [Big-O Cheat Sheet](http://www.bigocheatsheet.com/), PDF version can be download [here](http://www.bigocheatsheet.com/pdf/big-o-cheatsheet.pdf) or be found in this repo [here](./big-o-cheatsheet.pdf)
- Sergey, [Java Collections Complexity cheatsheet](https://gist.github.com/iSergius/e06963c6eca0a639023666097227427c), txt file can be found [here](./complexityjava.txt)
- Python Complexity Analysis, txt file can be found [here](complexitypython.txt)

<p align="center">
<span style="color:#1d58a6"><sup> &copy; Copyright Zhenye Na <img src="https://cdn3.iconfinder.com/data/icons/coffee-11/500/Coffee_brain-512.png" width="20" height="auto" /> May 2018 </sup></span>
</p>

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