leetcode-in-Java

This is leetcode solution in Java with eplaination and generalization.

LinkedList

#	Title	Solution	Difficulty	Source Code
2	Add Two Numbers	math	Medium	AddTwoNums.java
19	Remove Nth Node From End of List		Medium	RemoveNthNode.java
21	Merge Two Sorted Lists	loop and sort node	easy	MergeTwoSortedLists.java
23	Merge k Sorted Lists	Divide and Conquer + mergeTwoSortedLists	Hard	MergekSortedLists.java
24	Swap Nodes in Pairs	recursive + swap node	Medium	SwapNodesInPairs.java
61	Rotate List	connect tail and head & cut the right k places node	Medium	RotateList.java
82	Remove Duplicates from Sorted List II	find duplicate node and store duplicate state, update next pointer	Medium	RemoveDuplicatesFromSortedListII.java
83	Remove Duplicates from Sorted List	find duplicate node and update pointer next to next.next	Medium	RemoveDuplicatesFromSortedList.java
86	Partition List	Two Pointer	Medium	PartitionList.java
92	Reverse Linked List II	like Insertion Sort	Medium	ReverseLinkedListII.java
109	Convert Sorted List to Binary Search Tree	pre-order traversal	Medium	ConvertSortedListtoBST.java
138	Copy List with Random Pointer	recursive + hashmap	Medium	CopyListwithRandomPointer.java
141	Linked List Cycle	two pointer	Easy	LinkedListCycle.java
142	Linked List Cycle II	hashset or two pointer	Medium	LinkedListCycleII.java
143	Reorder List	reverse + connect	Medium	ReorderList.java
147	Insertion Sort List	insertion algorithm	Medium	InsertionSortList.java
148	Sort List	two pointer + merge sort algorithm	Medium	SortList.java
160	Intersection of Two Linked Lists	iteration	Medium	IntersectionofTwoLinkedLists.java
203	Remove Linked List Elements	slow pointer + connect	Easy	RemoveLinkedListElements.java
206	Reverse Linked List		Easy	ReverseLinkedList.java
234	Palindrome Linked List	reverse + equal	Easy	PalindromeLinkedList.java
328	Odd Even Linked List	connect next.next pointer	Medium	OddEvenLinkedList.java
430	Flatten a Multilevel Doubly Linked List		Medium	FlattenMultilevelDoublyLinkedList.java
445	Add Two Numbers II	reverse	Medium	AddTwoNumbersII.java
725	Split Linked List in Parts		Medium	SplitLinkedListinParts.java
817	Linked List Components		Medium	LinkedListComponents.java
876	Middle of the Linked List	two pointer	Easy	MiddleoftheLinkedList.java
1029	Next Greater Node In Linked List	stack	Medium	NextGreaterNodeInLinkedList.java

Tree

#	Title	Solution	Difficulty	Source Code
94	Binary Tree Inorder Traversal	stack or recursive	Medium	BinaryTreeInorderTraversal.java
95	Unique Binary Search Trees II	recursive	Medium	UniqueBinarySearchTreesII.java
96	Unique Binary Search Trees	dp	Medium	UniqueBinarySearchTrees.java
98	Validate Binary Search Tree	recursive or stack	Medium	ValidateBinarySearchTree.java
100	Same Tree	recursive	Easy	SameTree.java
101	Symmetric Tree	recursive	Easy	SymmetricTree.java
102	Binary Tree Level Order Traversal	recursive or bfs by queue	Medium	BinaryTreeLevelOrderTraversal.java
103	Binary Tree Zigzag Level Order Traversal	recursive or bfs by queue	Medium	BinaryTreeZigzagLevelOrderTraversal.java
104	Maximum Depth of Binary Tree	recursive	Easy	MaximumDepthofBinaryTree.java
105	Construct Binary Tree from Preorder and Inorder Traversal	hashmap + recursive	Medium	ConstructBinaryTreefromPreorderandInorderTraversal.java
106	Construct Binary Tree from Inorder and Postorder Traversal	hashmap + recursive	Medium	ConstructBinaryTreefromInorderandPostorderTraversal.java
107	Binary Tree Level Order Traversal II	recursive	Easy	BinaryTreeLevelOrderTraversalII.java
108	Convert Sorted Array to Binary Search Tree	preorder recursive	Easy	ConvertSortedArraytoBinarySearchTree.java
110	Balanced Binary Tree	recursive	Easy	BalancedBinaryTree.java
111	Minimum Depth of Binary Tree	recursive	Easy	MinimumDepthofBinaryTree.java
112	Path Sum	recursive	Easy	PathSum.java
113	Path Sum II	recursive	Medium	PathSumII.java
114	Flatten Binary Tree to Linked List	stack or recursive	Medium	FlattenBinaryTreetoLinkedList.java
116	Populating Next Right Pointers in Each Node	bfs by queue	Medium	PopulatingNextRightPointersinEachNode.java
117	Populating Next Right Pointers in Each Node II	bfs by queue	Medium	PopulatingNextRightPointersinEachNodeII.java
129	Sum Root to Leaf Numbers	stack or recursive	Medium	SumRoottoLeafNumbers.java
144	Binary Tree Preorder Traversal	stack or recursive	Medium	BinaryTreePreorderTraversal.java
199	Binary Tree Right Side View	queue or recursive	Medium	BinaryTreeRightSideView.java
222	Count Complete Tree Nodes	stack or recursive	Medium	CountCompleteTreeNodes.java
226	Invert Binary Tree	stack or recursive	Easy	InvertBinaryTree.java
230	Kth Smallest Element in a BST	stack or recursive	Medium	KthSmallestElementinaBST.java

Array

#	Title	Solution	Difficulty	Source Code

String

#	Title	Solution	Difficulty	Source Code

DP

#	Title	Solution	Difficulty	Source Code
5	Longest Palindromic Substring	dp	Medium	LongestPalindromicSubstring.java
62	Unique Paths	dp	Medium	UniquePaths.java
63	Unique Paths II	dp	Medium	UniquePathsII.java

Design

#	Title	Solution	Difficulty	Source Code
146	LRU Cache	HashMap + Double LinkedNode	Medium	LRUCache.java
155	Min Stack	Single LinkedNode or Stack(Java API)	easy	MinStack.java
173	Binary Search Tree Iterator	stack + preorder traversal	Medium	BinarySearchTreeIterator.java
208	Implement Trie (Prefix Tree)	array	Medium	ImplementTrie.java
211	Add and Search Word - Data structure design		Medium	AddAndSearchWord.java