zshouyi的博客

Let's play the minesweeper game (Wikipedia, online game)! You are given a 2D char matrix representing the game board. 'M' represents an unrevealed mine, 'E' represents an unrevealed empty squa

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 a nested list of integers, return the sum of all integers in the list weighted by their depth.Each element is either an integer, or a list -- whose elements may also be integers or other lis

Given a binary tree, find the leftmost value in the last row of the tree. Example 1:Input: 2 / \ 1 3Output:1Example 2: Input: 1 / \ 2 3

You need to find the largest value in each row of a binary tree.Example:Input: 1 / \ 3 2 / \ \ 5 3 9 Output: [1, 3, 9]层序遍历找每层的最大值。代码如下：

Given a binary tree, collect a tree's nodes as if you were doing this: Collect and remove all leaves, repeat until the tree is empty.Example:Given binary tree  1 / \

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

Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.An example is the root-to-leaf path 1->2->3 which represents the number 123.Find the tota

Given a string representing arbitrarily nested ternary expressions, calculate the result of the expression. You can always assume that the given expression is valid and only consists of digits 0-9, ?,

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 an m x n matrix of non-negative integers representing the height of each unit cell in a continent, the "Pacific ocean" touches the left and top edges of the matrix and the "Atlantic ocean" tou

Given n nodes labeled from 0 to n - 1 and a list of undirected edges (each edge is a pair of nodes), write a function to check whether these edges make up a valid tree.For example:Given n =

Given a picture consisting of black and white pixels, and a positive integer N, find the number of black pixels located at some specific row Rand column C that align with all the following rules:

Given a picture consisting of black and white pixels, find the number of black lonely pixels.The picture is represented by a 2D char array consisting of 'B' and 'W', which means black and white pi

Given a matrix consists of 0 and 1, find the distance of the nearest 0 for each cell.The distance between two adjacent cells is 1.Example 1: Input:0 0 00 1 00 0 0Output:0 0 00 1 00

There are N students in a class. Some of them are friends, while some are not. Their friendship is transitive in nature. For example, if A is a direct friend of B, and B is a direct friend of C, the

Given an integer array, your task is to find all the different possible increasing subsequences of the given array, and the length of an increasing subsequence should be at least 2 .Example:In

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

There is a ball in a maze with empty spaces and walls. The ball can go through empty spaces by rolling up, down, left or right, but it won't stop rolling until hitting a wall. When the ball stops, i

There is a ball in a maze with empty spaces and walls. The ball can go through empty spaces by rolling up, down, left or right, but it won't stop rolling until hitting a wall. When the ball stops, i

Given n nodes labeled from 0 to n - 1 and a list of undirected edges (each edge is a pair of nodes), write a function to find the number of connected components in an undirected graph.Example 1:

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

Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST.第一种方法，把linkedlist转化成arraylist，使用二分法构建BST。代码如下：/** * Definition for singly-linked lis

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 ea

Given inorder and postorder traversal of a tree, construct the binary tree.Note:You may assume that duplicates do not exist in the tree.首先参考这篇博文：Construct Binary Tree From Inorder and Preord

Given two binary trees, write a function to check if they are equal or not.Two binary trees are considered equal if they are structurally identical and the nodes have the same value.递归求解比较简单，遍历过

Given a binary tree, find its maximum depth.The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.这道题用递归比较好做，代码如下：/** * Definition

Given a nested list of integers, return the sum of all integers in the list weighted by their depth.Each element is either an integer, or a list -- whose elements may also be integers or other lis

Given a binary tree, find its minimum depth.The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.这里用递归解法，分了5种返回情况，详见代码，代码如下：/** *

Given a binary tree, return all root-to-leaf paths.For example, given the following binary tree: 1 / \2 3 \ 5All root-to-leaf paths are:["1->2->5", "1->3"]Cre

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.For example:Given the below binary tree and sum

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).For example, this binary tree [1,2,2,3,4,4,3] is symmetric: 1 / \ 2 2 / \ / \3 4 4 3

Given an array where elements are sorted in ascending order, convert it to a height balanced BST.这道题用递归的解法，每次选数组中间的数作为node，可以保证最后是一个height balanced BST。代码如下：/** * Definition for a binary tree n

Given preorder and inorder traversal of a tree, construct the binary tree.Note:You may assume that duplicates do not exist in the tree.首先参考这篇博文：Construct Binary Tree From Inorder and Preorde

Given a positive integer n, find the least number of perfect square numbers (for example, 1, 4, 9, 16, ...) which sum to n.For example, given n = 12, return 3 because 12 = 4 + 4 + 4; given n =

Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.For example:Given the below binary tree and sum = 22, 5 / \

Follow up for problem "Populating Next Right Pointers in Each Node".What if the given tree could be any binary tree? Would your previous solution still work?Note:You may only use constant

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

The thief has found himself a new place for his thievery again. There is only one entrance to this area, called the "root." Besides the root, each house has one and only one parent house. After a tour

Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.For example:Given the following binary tree, 1