Leetcode solutions in Java

My accepted leetcode solutions to some of the common interview problems.

Array

• Pascals Traiangle II (Easy) solved
• Product Of Array Except Self (Medium)solved
• Rotate Matrix (Medium) pending
• Set Matrix Zeroes (Medium)

The key point is how to minimize the space complexity

• Third Maximum Number (Easy)
• Two Sum (Easy)
• TwoSum II (Easy)
• Can Place Flowers (Easy)
• Merge Intervals (Medium)

turn arraylist into array: merged.toArray(new int[merged.size()][2]);

• First Missing Positive (Hard)
• Fruit Into Baskets (Medium)

How to slove it with stack?

• MaxProduct Of Three Numbers (Easy)
• Missing Number (Easy)
  in case of overflow

int missingNumber(vector<int>& nums) {
    int result = 0
    for (int i = 0; i < nums.size(); ++i) 
        result += (i+1)-nums[i];
    }
    return result;
}

• Merge Sorted Array (Easy)
• Rotate Array (Easy)
• Sort Colors (Medium)
• Battleships in a Board (Medium) sloved
• Find the Celebrity (Medium)
• Meeting Rooms (Easy)
• Longest Continuous Increasing Subsequence (Easy)
• Sparse Matrix Multiplication (Medium)
• Read N Characters Given Read4 (Easy)
• Maximum Swap (Medium)
• H-Index (Medium)
• Insert Interval (Hard)
• Increasing Triplet Subsequence (Medium)
• K Empty Slots (Hard)
• Subarray Sum Equals K (Medium)
• Pour Water (Medium)
• Relative Ranks (Easy)
• Next Greater Element I (Easy)
• Largest Number At Least Twice of Others (Easy)
• Minimum Moves to Equal Array Elements II (Median)
• Image Smoother (Easy)
• Minimum Index Sum of Two Lists (Easy)
• Card Flipping Game (Medium)
• Employee Free Time (Hard)
• Best Meeting Point (Hard)
• My Calendar III (Hard)
• Champagne Tower (Medium)
• Valid Tic-Tac-Toe State (Medium)
• Number of Subarrays with Bounded Maximum (Medium)
• Surface Area of 3D Shapes (Easy)
• Max Consecutive Ones (Easy)
• Max Consecutive Ones II (Medium)
• Add to Array-Form of Integer (Easy)
• Find Pivot Index (Easy)
• Largest Time for Given Digits (Easy)
• Minimum Time Difference (Medium)
• Reveal Cards In Increasing Order (Medium)
• Sort Array By Parity II (Easy)
• Matrix Cells in Distance Order (Easy)
• Maximum Sum of Two Non-Overlapping Subarrays (Medium)
• Longest Line of Consecutive One in Matrix (Medium)
• Array Partition I (Easy)

Backtracking

• Combinations (Medium)
• Combinations Sum (Medium)
• Combinations Sum II (Medium)
• Letter Phone Number (Medium)
• Paliandrome Partitioning (Medium)
• Permutations (Medium)
• Permutations II (Medium)
• SubSets (Medium)
• SubSet II (Medium)
• Word Search (Medium)
• Word Search II (Hard)
• Generate Parentheses (Medium)
• Remove Invalid Parentheses (Hard)
• Regular Expression Matching (Hard)
• Expression Add Operators (Hard)
• Wildcard Matching (Hard)
• Letter Case Permutation (Easy)
• Zuma Game (Hard)
• Matchsticks to Square (Medium)

Binary Search

• Minimum Sorted Rotated Array (Medium)
• Search in a Rotated Sorted Array (Medium)
• Search for a Range (Medium)
• Sqrt(x) (Easy)
• Search Insert Position (Easy)
• Median of Two Sorted Arrays (Hard)
• Pow(x, n) (Medium)
• Find Peak Element (Medium)
• Target Sum (Medium)
• H-Index II (Medium)
• Swim in Rising Water (Hard)
• Time Based Key-Value Store (Medium)
• Minimum Window Subsequence (Hard)
• Koko Eating Bananas (Hard)

Bit Manipulation

• Gray Code (Medium)
• Hamming Distance (Easy)
• Total Hamming Distance (Medium)
• Divide Two Integers (Medium)
• Binary Number with Alternating Bits (Easy)

Breadth First Search

• Binaray Tree Level Order Traversal (Medium)
• Word Ladder (Medium)
• Word Ladder II (Hard)
• Walls and Gates (Medium)
• Open the lock (Medium)
• Cut Off Trees for Golf Event (Hard)
• Race Car (Hard)
• Bus Routes (Hard)
• Sliding Puzzle (Hard)
• Matrix (Medium)

Depth First Search

• Minesweeper (Medium)
• Movie Recommend (Medium)
• Number Of Islands (Medium)
• Course Schedule (Medium)
• Course Schedule II (Medium)
• Alien Dictionary (Hard)
• Graph Valid Tree (Medium)
• Longest Consecutive Sequence (Hard)
• Accounts Merge (Medium)
• CloneGraph (Medium)
• Island Perimeter (Easy)
• Number of Distinct Islands (Medium)
• Number of Distinct Islands II (Hard)
• Smallest Rectangle Enclosing Black Pixels (Hard)
• Bricks Falling When Hit (Hard)
• Robot Room Cleaner (Hard)
• Cracking the Safe (Hard)
• All Paths From Source to Target (Medium)
• Max Area of Island (Medium)
• Satisfiability of Equality Equations (Medium)
• Number of Enclaves (Medium)
• As Far from Land as Possible (Medium)
• Minimize Malware Spread (Hard)

Design

• Copy List With Random Pointer (Medium)
• Encode and Decode Tiny URL (Medium)
• LFU Cache (Hard)
• LRU Cache (Hard)
• Insert Delete Get Random (Medium)
• Serialize Deserialize Binary Tree (Hard)
• Design Twitter (Medium)
• Tic-Tac-Toe (Medium)
• Implement Trie (Prefix Tree) (Medium)
• Binary Search Tree Iterator (Medium)
• Design Search Autocomplete System (Hard)
• Design Excel Sum Formula (Hard)
• Flatten Nested List Iterator (Medium)
• Add and Search Word - Data structure design (Medium)
• Prefix and Suffix Search (Hard)
• Insert Delete GetRandom O(1) - Duplicates allowed (Hard)

Divide and Conquer

• Kth Largest Element In a Array (Medium)
• Reverse Pairs (Hard)
• Search in a 2D Matrix (Medium)
• 24 Game (Hard)
• Reverse Pairs II (Hard)

Dynamic Programming

• Best Time To Buy and Sell Stocks (Easy)
• Best Time to Buy and Sell Stock III (Hard)
• Best Time to Buy and Sell Stock with Transaction Fee (Medium)
• Climbing Stairs (Easy)
• Coin Change (Medium)
• Coin Change 2 (Medium)
• Decode Ways (Medium)
• House Robber (Easy)
• House Robber II (Medium)
• Longest Increasing Subsequence (Medium)
• Longest Paliandromic Substring (Medium)
• Longest Palindromic Subsequence (Medium)
• Maximum Product Subarray (Medium)
• Min Cost Climbing Stairs (Easy)
• Palindrome Partitioning II (Hard)
• UniqueBinary Search Trees (Medium)
• Unique Binary Search Trees II (Medium)
• WordBreak (Medium)
• WordBreak II (Hard)
• Concatenated Words (Hard)
• Can I Win (Medium)
• Maximum Subarray (Easy)
• Dungeon Game (Hard)
• 2 Keys Keyboard (Medium)
• Maximum Sum of 3 Non-Overlapping Subarrays (Hard)
• Maximal Square (Medium)
• Continuous Subarray Sum (Medium)
• Decode Ways II (Hard)
• Palindromic Substrings (Medium)
• Number of Longest Increasing Subsequence (Medium)
• Combination Sum IV (Medium)
• Paint House II (Hard)
• Split Array Largest Sum (Hard)
• Number Of Corner Rectangles (Medium)
• Burst Balloons (Hard)
• Largest Plus Sign (Medium)
• Palindrome Pairs (Hard)
• Cherry Pickup (Hard)
• Knight Probability in Chessboard (Medium)
• Largest Sum of Averages (Medium)
• Minimum Number of Refueling Stops (Hard)
• Cat and Mouse (Hard)
• Stone Game (Medium)
• Odd Even Jump (Hard)
• Profitable Schemes (Hard)
• Maximum Vacation Days (Hard)
• Russian Doll Envelopes (Hard)
• Student Attendance Record II (Hard)
• Out of Boundary Paths (Medium)
• Remove Boxes (Hard)
• Stickers to Spell Word (Hard)
• Ones and Zeroes (Medium)
• Encode String with Shortest Length (Hard)
• Length of Longest Fibonacci Subsequence (Medium)
• Encode String with Shortest Length (Hard)

Greedy

• Jump Game (Medium)
• Jump Game II (Hard)
• Course Schedule III (Medium)
• GasStation (Medium)
• Non-Overlapping Intervals (Medium)
• Minimum Number of Arrows to Burst Balloons (Medium)
• Queue Reconstruction By Height (Medium)
• Task Scheduler (Medium)
• Maximum Length of Pair Chain (Medium)
• Lemonade Change (Easy)
• Score After Flipping Matrix (Medium)
• IPO (Hard)
• String Without AAA or BBB (Medium)
• Boats to Save People (Medium)
• Broken Calculator (Medium)
• Two City Scheduling (Easy)

Hashing

• Anagrams (Medium)
• Group Anagrams (Medium)
• Kdiff Pairs In a Array (Easy)
• Sort Character by Frequency (Medium)
• Two Sum (Easy)
• Valid Anagram (Easy)
• Maximum Size Subarray Sum Equals k (Medium)
• Contiguous Array (Medium)
• Brick Wall (Medium)
• Partition Labels (Medium)
• Custom Sort String (Medium)
• Short Encoding of Words (Medium)
• Substring with Concatenation of All Words (Hard)
• Distribute Candies (Easy)
• Groups of Special-Equivalent Strings (Easy)
• Number of Atoms (Hard)

Heap

• Sliding Window Maximum (Hard)
• The Skyline Problem (Hard)
• Meeting Rooms II (Medium)
• Top K Frequent Words (Medium)
• Candy (Hard)
• Smallest Rotation with Highest Score (Hard)
• Maximum Frequency Stack (Hard)
• Reachable Nodes In Subdivided Graph (Hard)

Linked List

• Intersection of two Linked-Lists (Easy)
• Linked List Cycle (Easy)
• Merge K Sorted Lists (Hard)
• Merge Two Sorted List (Easy)
• Paliandrome List (Easy)
• Reverse Linked List (Easy)
• Delete Node in a Linked List (Easy)
• Reverse Nodes in k-Group (Hard)
• Swap Nodes in Pairs (Medium)
• Middle of Linked List (Easy)
• Split Linked List in Parts (Medium)
• Next Greater Node In Linked List (Medium)

Math

• Add Two Numbers (Medium)
• Count Primes (Easy)
• Rotate Function (Medium)
• Water and Jug Problem (Medium)
• Add Digits (Easy)
• Excel Sheet Column Title (Easy)
• Roman to Integer (Easy)
• Bulb Switcher II (Medium)
• Global and Local Inversions (Medium)
• Solve the Equation (Medium)
• Couples Holding Hands (Hard)
• Reaching Points (Hard)
• Nth Magical Number (Hard)
• Squirrel Simulation (Medium)
• Projection Area of 3D Shapes (Easy)
• Decoded String at Index (Medium)
• Base 7 (Easy)
• Smallest Range I (Easy)
• Largest Component Size by Common Factor (Hard)

Reservoir Sampling

• Random Pick Index (Medium)

Stack

• Min Stack (Easy)
• Valid Parentheses (Easy)
• Largest Rectangle In Histogram (Hard)
• Implement Queue using Stacks (Easy)
• Maximal Rectangle (Hard)
• Exclusive Time of Functions (Medium)
• Basic Calculator (Hard)
• Decode String (Medium)
• Longest Valid Parentheses (Hard)

String

• First Unique Character In a String (Easy)
• Repeated Substring Pattern (Easy)
• Reverse Words In a String (Medium)
• ReverseWords II (Medium)
• String to Integer (Medium)
• Text Justification (Hard)
• ZigZag Conversion (Medium)
• Implement StrStr (Easy)
• Excel Sheet Column Number (Easy)
• Compare Version Numbers (Easy)
• Valid Palindrome (Easy)
• Simplify Path (Medium)
• Permutation in String (Medium)
• Add Binary (Easy)
• Valid Palindrome II (Easy)
• One Edit Distance (Medium)
• Count and Say (Easy)
• Multiply Strings (Medium)
• Longest Word in Dictionary through Deleting (Medium)
• Isomorphic Strings (Easy)
• String Compression (Easy)
• Longest Common Prefix (Easy)
• Find the Closest Palindrome (Hard)
• Monotone Increasing Digits (Medium)
• Shortest Palindrome (Hard)
• Valid Word Abbreviation (Easy)
• Longest Palindrome (Easy)
• Replace Words (Medium)
• Rotate String (Easy)
• Keyboard Row (Easy)
• Student Attendance Record I (Easy)
• Split Concatenated Strings (Medium)
• Valid Word Square (Easy)
• Reconstruct Original Digits from English (Medium)
• Push Dominoes (Medium)
• Validate IP Address (Medium)
• Reverse String II (Easy)
• Find Words That Can Be Formed by Characters (Easy)
• Minimum Add to Make Parentheses Valid (Medium)

Tree

• Binaray Tree Right Side View (Medium)
• Binary Tree Maximum Path Sum (Hard)
• Boundary of Binary Tree (Medium)
• Convert sorted array to BST (Medium)
• Lowest Common Ancestor of a Binary Tree (Medium)
• Lowest Common Ancestor of a BST (Easy)
• Most Frequent Subtree Sum (Medium)
• Path Sum III (Easy)
• Convert Postorder and Inorder traversal to Binary Tree (Medium)
• Convert Preorder and Inorder traversal to Binary Tree (Medium)
• Sorted Array to BST (Medium)
• Valid Binary Search Tree (Medium)
• Largest BST Subtree (Medium)
• Closest Binary Search Tree Value (Easy)
• Inorder Successor in BST (Medium)
• Construct String From Binary Tree (Easy)
• Flatten Binary Tree to Linked List (Medium)
• Populating Next Right Pointers in Each Node (Medium)
• Populating Next Right Pointers in Each Node II (Medium)
• Subtree of Another Tree (Easy)
• Binary Tree Zigzag Level Order Traversal (Medium)
• Binary Tree Inorder Traversal (Medium)
• Symmetric Tree (Easy)
• Maximum Binary Tree (Medium)
• Find Bottom Left Tree Value (Medium)
• Diameter of Binary Tree (Easy)
• Binary Tree Paths (Easy)
• Sum of Left Leaves (Easy)
• Two Sum IV - Input is a BST (Easy)
• Average of Levels in Binary Tree (Easy)
• Convert Binary Search Tree to Sorted Doubly Linked List (Easy)
• Same Tree (Easy)
• Binary Tree Longest Consecutive SequencefindMinDifference II (Medium)
• Minimum Absolute Difference in BST (Medium)
• Equal Tree Partition (Medium)
• Split BST (Medium)
• Closest Leaf in a Binary Tree (Medium)
• Maximum Width of Binary Tree (Medium)
• Recover Binary Search Tree (Hard)
• Binary Tree Postorder Traversal (Hard)
• Serialize and Deserialize N-ary Tree (Hard)
• Convert BST to Greater Tree (Easy)
• All Nodes Distance K in Binary Tree (Medium)
• All Possible Full Binary Trees (Medium)
• Flip Equivalent Binary Trees (Medium)
• Construct Binary Tree from String (Medium)
• Find Largest Value in Each Tree Row (Medium)
• Find Bottom Left Tree Value (Medium)
• Maximum Level Sum of a Binary Tree (Medium)
• Leaf-Similar Trees (Easy)
• Binary Tree Tilt (Easy)

Two Pointers

• Four Sum (Medium)
• Longest Substring Witout Repeats (Medium)
• Three Sum (Medium)
• Trapping Rain Water (Hard)
• 3Sum Closest (Medium)
• Move Zeroes (Easy)
• Remove Duplicates (Easy)
• Remove Duplicates II (Medium)
• Minimum Size Subarray Sum (Medium)
• Minimum Window Substring (Hard)
• Smallest Range (Hard)
• Subarray Product Less Than K (Medium)
• Number of Matching Subsequences (Medium)
• Subarrays with K Different Integers (Hard)
• Last Substring in Lexicographical Order (Hard)