Skip to content

kumar-abhishek/leetcode

BranchesTags
 
 

Folders and files

NameName
Last commit message
Last commit date

Latest commit

 

History

416 Commits

doc

doc

 
 

lib

lib

 
 

src

src

 
 

test

test

 
 

.gitignore

.gitignore

 
 

.travis.yml

.travis.yml

 
 

README.md

README.md

 
 

build.xml

build.xml

 
 

Repository files navigation

Solutions, unit tests, and code skeletons for problems from Leetcode OJ. (in progress)

Build Status Coverage Status

  root
    |--- doc
    |     |-- category.md   // category for problems in leetcode
    |     |-- problems.tsv  // searchable tsv file listing problems from leetcode
    |     |-- road.md       // general things I learnt through the process
    |--- lib
    |     |-- *.jar         // jar file referenced in this project
    |--- src   // solutions for problems
    |     |-- _001_TwoSum
    |     |         |-- Practice.java    // code skeleton
    |     |         |-- Solution.java
    |     |         |-- Solution*.java   // other solutions for this problem
    |     |-- ......
    |--- test  // unit tests
    |     |-- _001_TwoSum
    |     |         |-- PracticeTest.java 
    |     |         |-- SolutionTest.java
    |     |         |-- Solution*Test.java
    |     |-- ......
  • Discussions and code reviews are more than welcome.
  • Solution.java provides OJ-accepted solution.
  • Practice.java provides code skeleton for each problem
  • SolutionTest.java and PracticeTest.java provides basic unit tests to verify your solution.

P.S.:

  • Please use Java 8 to compile and run
  • Many solutions are from online sources, like Leetcode OJ discussion, coders' blogs, etc.
  • Solution that passed unit tests does not guarantee to pass Leetcode OJ.
# Problem Difficulty Tags Note
001 Two Sum Medium Array Hash Table O(N^2) -> O(N) + O(N) hashtable
002 Add Two Numbers Medium Linked List Math
003 Longest Substring Without Repeating Characters Medium Hash Table Two Pointers String two pointers to keep window -> O(N)
004 Median of Two Sorted Arrays Hard Divide and Conquer Array Binary Search
005 Longest Palindromic Substring Medium String expanding two pointers
006 ZigZag Conversion Easy String
007 Reverse Integer Easy Math How to monitor Stack Overflow
008 String to Integer (atoi) Easy Math String
009 Palindrome Number Easy Math 1) count digits; 2) get digit from number's front/back; 3) to avoid StackOverflow, only reverse half part of number
010 Regular Expression Matching Hard Dynamic Programming Backtracking String finite state machine!
011 Container With Most Water Medium Array Two Pointers narrowing two pointers
012 Integer to Roman Medium Math String
013 Roman to Integer Easy Math String
014 Longest Common Prefix Easy String
015 3Sum Medium Array Two Pointers sorting then 2sum
016 3Sum Closest Medium Array Two Pointers
017 Letter Combinations of a Phone Number Medium Backtracking String BFS: iterative V.S. DFS: backtracking
018 4Sum Medium Array Hash Table Two Pointers
019 Remove Nth Node From End of List Easy Linked List Two Pointers fast-slow two pointers on Linked List
020 Valid Parentheses Easy Stack String stack basic, corner case
021 Merge Two Sorted Lists Easy Linked List
022 Generate Parentheses Medium Backtracking String BT template
023 Merge k Sorted Lists Hard Divide and Conquer Linked List Heap
024 Swap Nodes in Pairs Medium Linked List
025 Reverse Nodes in k-Group Hard Linked List
026 Remove Duplicates from Sorted Array Easy Array Two Pointers partition techinque on array
027 Remove Element Easy Array Two Pointers
028 Implement strStr() Easy Two Pointers String
029 Divide Two Integers Medium Math Binary Search !
030 Substring with Concatenation of All Words Hard Hash Table Two Pointers String
031 Next Permutation Medium Array
032 Longest Valid Parentheses Hard Dynamic Programming String DP
033 Search in Rotated Sorted Array Hard Array Binary Search
034 Search for a Range Medium Array Binary Search ! one binary search to find start position, and another one find ending position
035 Search Insert Position Medium Array Binary Search standard binary search with minor modification
036 Valid Sudoku Easy Hash Table
037 Sudoku Solver Hard Backtracking Hash Table
038 Count and Say Easy String
039 Combination Sum Medium Array Backtracking BT template + prune siblings
040 Combination Sum II Medium Array Backtracking BT template + prune siblings + skip duplicate
041 First Missing Positive Hard Array swap-until technique
042 Trapping Rain Water Hard Array Stack Two Pointers !!
043 Multiply Strings Medium Math String ! simulate multiplication
044 Wildcard Matching Hard Dynamic Programming Backtracking Greedy String
045 Jump Game II Hard Array Greedy
046 Permutations Medium Backtracking backtrack template + select to add
047 Permutations II Hard Backtracking backtrack template + select to add + skip duplicate using set
048 Rotate Image Medium Array
049 Group Anagrams Medium Hash Table String !!
050 Pow(x, n) Medium Math Binary Search
051 N-Queens Hard Backtracking
052 N-Queens II Hard Backtracking
053 Maximum Subarray Medium Divide and Conquer Array Dynamic Programming
054 Spiral Matrix Medium Array
055 Jump Game Medium Array Greedy
056 Merge Intervals Hard Array Sort how to decide the boundary of merged interval
057 Insert Interval Hard Array Sort ! enlarge to merge interval
058 Length of Last Word Easy String
059 Spiral Matrix II Medium Array
060 Permutation Sequence Medium Backtracking Math
061 Rotate List Medium Linked List Two Pointers fast-slow pointers; [189] Rotate Array
062 Unique Paths Medium Array Dynamic Programming
063 Unique Paths II Medium Array Dynamic Programming
064 Minimum Path Sum Medium Array Dynamic Programming
065 Valid Number Hard Math String
066 Plus One Easy Array Math
067 Add Binary Easy Math String add binary numbers
068 Text Justification Hard String ! very careful string operations
069 Sqrt(x) Medium Math Binary Search !binary search along y-axle
070 Climbing Stairs Easy Dynamic Programming
071 Simplify Path Medium Stack String
072 Edit Distance Hard Dynamic Programming String
073 Set Matrix Zeroes Medium Array
074 Search a 2D Matrix Medium Array Binary Search 2D coordidates --> 1D index
075 Sort Colors Medium Array Two Pointers Sort
076 Minimum Window Substring Hard Hash Table Two Pointers String ![substring/sublist] hashing + two pointers -> O(N)
077 Combinations Medium Backtracking
078 Subsets Medium Array Backtracking Bit Manipulation backtrack template (see README)
079 Word Search Medium Array Backtracking
080 Remove Duplicates from Sorted Array II Medium Array Two Pointers from 2 to k (general)
081 Search in Rotated Sorted Array II Medium Array Binary Search
082 Remove Duplicates from Sorted List II Medium Linked List
083 Remove Duplicates from Sorted List Easy Linked List
084 Largest Rectangle in Histogram Hard Array Stack
085 Maximal Rectangle Hard Array Hash Table Stack Dynamic Programming
086 Partition List Medium Linked List Two Pointers
087 Scramble String Hard Dynamic Programming String
088 Merge Sorted Array Easy Array Two Pointers in-place merging -> from end to begin; two pointers on two lists
089 Gray Code Medium Backtracking
090 Subsets II Medium Array Backtracking backtrack template + skip duplicate
091 Decode Ways Medium Dynamic Programming String
092 Reverse Linked List II Medium Linked List
093 Restore IP Addresses Medium Backtracking String
094 Binary Tree Inorder Traversal Medium Tree Hash Table Stack
095 Unique Binary Search Trees II Medium Tree Dynamic Programming
096 Unique Binary Search Trees Medium Tree Dynamic Programming
097 Interleaving String Hard Dynamic Programming String
098 Validate Binary Search Tree Medium Tree Depth-first Search
099 Recover Binary Search Tree Hard Tree Depth-first Search
100 Same Tree Easy Tree Depth-first Search
101 Symmetric Tree Easy Tree Depth-first Search
102 Binary Tree Level Order Traversal Easy Tree Breadth-first Search
103 Binary Tree Zigzag Level Order Traversal Medium Tree Breadth-first Search Stack
104 Maximum Depth of Binary Tree Easy Tree Depth-first Search
105 Construct Binary Tree from Preorder and Inorder Traversal Medium Tree Array Depth-first Search
106 Construct Binary Tree from Inorder and Postorder Traversal Medium Tree Array Depth-first Search
107 Binary Tree Level Order Traversal II Easy Tree Breadth-first Search
108 Convert Sorted Array to Binary Search Tree Medium Tree Depth-first Search
109 Convert Sorted List to Binary Search Tree Medium Depth-first Search Linked List
110 Balanced Binary Tree Easy Tree Depth-first Search
111 Minimum Depth of Binary Tree Easy Tree Depth-first Search Breadth-first Search
112 Path Sum Easy Tree Depth-first Search
113 Path Sum II Medium Tree Depth-first Search
114 Flatten Binary Tree to Linked List Medium Tree Depth-first Search
115 Distinct Subsequences Hard Dynamic Programming String
116 Populating Next Right Pointers in Each Node Medium Tree Depth-first Search
117 Populating Next Right Pointers in Each Node II Hard Tree Depth-first Search
118 Pascal's Triangle Easy Array
119 Pascal's Triangle II Easy Array
120 Triangle Medium Array Dynamic Programming
121 Best Time to Buy and Sell Stock Medium Array Dynamic Programming
122 Best Time to Buy and Sell Stock II Medium Array Greedy
123 Best Time to Buy and Sell Stock III Hard Array Dynamic Programming
124 Binary Tree Maximum Path Sum Hard Tree Depth-first Search post-order, local and global , README
125 Valid Palindrome Easy Two Pointers String
126 Word Ladder II Hard Array Backtracking Breadth-first Search String
127 Word Ladder Medium Breadth-first Search
128 Longest Consecutive Sequence Hard Array
129 Sum Root to Leaf Numbers Medium Tree Depth-first Search
130 Surrounded Regions Medium Breadth-first Search
131 Palindrome Partitioning Medium Backtracking
132 Palindrome Partitioning II Hard Dynamic Programming
133 Clone Graph Medium Depth-first Search Breadth-first Search Graph DFS V.S. BFS
134 Gas Station Medium Greedy
135 Candy Hard Greedy
136 Single Number Medium Hash Table Bit Manipulation
137 Single Number II Medium Bit Manipulation
138 Copy List with Random Pointer Hard Hash Table Linked List
139 Word Break Medium Dynamic Programming
140 Word Break II Hard Dynamic Programming Backtracking
141 Linked List Cycle Medium Linked List Two Pointers
142 Linked List Cycle II Medium Linked List Two Pointers
143 Reorder List Medium Linked List
144 Binary Tree Preorder Traversal Medium Tree Stack
145 Binary Tree Postorder Traversal Hard Tree Stack
146 LRU Cache Hard Data Structure
147 Insertion Sort List Medium Linked List Sort
148 Sort List Medium Linked List Sort ! fast-slow to find middle + iterative reverse + merge sort
149 Max Points on a Line Hard Hash Table Math
150 Evaluate Reverse Polish Notation Medium Stack
151 Reverse Words in a String Medium String README
152 Maximum Product Subarray Medium Array Dynamic Programming
153 Find Minimum in Rotated Sorted Array Medium Array Binary Search
154 Find Minimum in Rotated Sorted Array II Hard Array Binary Search
155 Min Stack Easy Stack Data Structure
157 Read N Characters Given Read4 Easy String
158 Read N Characters Given Read4 II Hard String
160 Intersection of Two Linked Lists Easy Linked List two pointers on two lists; combine long and short lists into one
161 One Edit Distance Medium String
162 Find Peak Element Medium Array Binary Search
164 Maximum Gap Hard Sort
165 Compare Version Numbers Easy String
166 Fraction to Recurring Decimal Medium Hash Table Math
168 Excel Sheet Column Title Easy Math convert decimal to other BASE system
169 Majority Element Easy Divide and Conquer Array Bit Manipulation
171 Excel Sheet Column Number Easy Math convert other BASE system to decimal system
172 Factorial Trailing Zeroes Easy Math count the number of certain number (e.g. 5) in n!
173 Binary Search Tree Iterator Medium Tree Stack
174 Dungeon Game Hard Dynamic Programming Binary Search
179 Largest Number Medium Sort
186 Reverse words in a string II Medium Array two pass + include last position trick
187 Repeated DNA Sequences Medium Hash Table Bit Manipulation
188 Best Time to Buy and Sell Stock IV Hard Dynamic Programming
189 Rotate Array Easy Array
190 Reverse Bits Easy Bit Manipulation
191 Number of 1 Bits Easy Bit Manipulation
198 House Robber Easy Dynamic Programming
199 Binary Tree Right Side View Medium Tree Depth-first Search Breadth-first Search
200 Number of Islands Medium Depth-first Search Breadth-first Search
201 Bitwise AND of Numbers Range Medium Bit Manipulation
202 Happy Number Easy Hash Table Math
203 Remove Linked List Elements Easy Linked List
204 Count Primes Easy Hash Table Math sieve algorithm
205 Isomorphic Strings Easy Hash Table
206 Reverse Linked List Easy Linked List
207 Course Schedule Medium Depth-first Search Breadth-first Search Graph Topological Sort
208 Implement Trie (Prefix Tree) Medium Data Structure Trie
209 Minimum Size Subarray Sum Medium Array Two Pointers Binary Search
210 Course Schedule II Medium Depth-first Search Breadth-first Search Graph Topological Sort
211 Add and Search Word - Data structure design Medium Backtracking Data Structure Trie
212 Word Search II Hard Backtracking Trie
213 House Robber II Medium Dynamic Programming
214 Shortest Palindrome Hard String
215 Kth Largest Element in an Array Medium Divide and Conquer Heap max-heap using Java's Priority Queue
216 Combination Sum III Medium Array Backtracking
217 Contains Duplicate Easy Array Hash Table
218 The Skyline Problem Hard Divide and Conquer Heap
219 Contains Duplicate II Easy Array Hash Table
220 Contains Duplicate III Medium Binary Search Tree
221 Maximal Square Medium Dynamic Programming
222 Count Complete Tree Nodes Medium Tree Binary Search
223 Rectangle Area Easy Math
224 Basic Calculator Medium Stack Math
225 Implement Stack using Queues Easy Stack Data Structure
226 Invert Binary Tree Easy Tree
227 Basic Calculator II Medium String
228 Summary Ranges Easy Array
229 Majority Element II Medium Array !vote algorithm
230 Kth Smallest Element in a BST Medium Tree Binary Search
231 Power of Two Easy Math Bit Manipulation
232 Implement Queue using Stacks Easy Stack Data Structure README
233 Number of Digit One Medium Math
234 Palindrome Linked List Easy Linked List Two Pointers
235 Lowest Common Ancestor of a Binary Search Tree Easy Tree
236 Lowest Common Ancestor of a Binary Tree Medium Tree README
237 Delete Node in a Linked List Easy Linked List
238 Product of Array Except Self Medium Array
239 Sliding Window Maximum Hard Heap descending queue
240 Search a 2D Matrix II Medium Divide and Conquer Binary Search
241 Different Ways to Add Parentheses Medium Divide and Conquer
242 Valid Anagram Easy Hash Table Sort
251 Flatten2DVector Medium Design
252 Meeting Rooms Easy Sort
253 Meeting Rooms II Medium Heap Greedy Sort
257 Binary Tree Paths Easy Tree
258 Add Digits Easy Math
260 Single Number III Medium Bit Manipulation
261 Graph Valid Tree Medium Breadth-first Search Depth-first Search Graph Union-Find
263 Ugly Number Easy Math
264 Ugly Number II Medium Math Heap
268 Missing Number Medium Array Math Bit Manipulation
269 Alien Dictionary Hard Graph Topological Sort BFS
273 Integer to English Words Medium Math String
274 H-Index Medium Hash Table Sort
275 H-Index II Medium Binary Search
278 First Bad Version Easy Binary Search
279 Perfect Squares Medium Dynamic Programming Breadth-first Search Math
282 Expression Add Operators Hard Divide and Conquer
283 Move Zeroes Easy Array Two Pointers
284 Peeking Iterator Medium Design
286 Walls And Gates Medium BFS
287 Find the Duplicate Number Hard Array Two Pointers Binary Search

About

Leetcode solutions, code skeletons, and unit tests in Java (in progress)

Resources

Readme
Activity

Stars

0 stars

Watchers

3 watching

Forks

0 forks
Report repository

Releases

No releases published

Packages

No packages published

Languages

  • Java 100.0%