Yingying

Given inorder and postorder traversal of a tree, construct the binary tree.Note:You may assume that duplicates do not exist in the tree.Recursive：public class Solution { public TreeNod

Given a 2d grid map of '1's (land) and '0's (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assu

Given an encoded string, return it's decoded string.The encoding rule is: k[encoded_string], where the encoded_stringinside the square brackets is being repeated exactly k times. Note thatk is g

Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors.OJ's undirected graph serialization:Nodes are labeled uniquely.We use # as a separator for each

Given a binary tree, determine if it is a valid binary search tree (BST).Assume a BST is defined as follows:The left subtree of a node contains only nodes with keys less than the node's key.Th

There are a total of n courses you have to take, labeled from 0 to n - 1.Some courses may have prerequisites, for example to take course 0 you have to first take course 1, which is expressed as

There are a total of n courses you have to take, labeled from 0 to n - 1.Some courses may have prerequisites, for example to take course 0 you have to first take course 1, which is expressed as

Remember the story of Little Match Girl? By now, you know exactly what matchsticks the little match girl has, please find out a way you can make one square by using up all those matchsticks. You shoul

Given a list of airline tickets represented by pairs of departure and arrival airports [from, to], reconstruct the itinerary in order. All of the tickets belong to a man who departs from JFK. Thus,

Given a 2D board containing 'X' and 'O' (the letter O), capture all regions surrounded by 'X'.A region is captured by flipping all 'O's into 'X's in that surrounded region.For example,