427. 建立四叉树 我们想要使用一棵四叉树来储存一个 N x N 的布尔值网络.网络中每一格的值只会是真或假.树的根结点代表整个网络.对于每个结点, 它将被分等成四个孩子结点直到这个区域内的值都是相同的. 每个结点还有另外两个布尔变量: isLeaf 和 val.isLeaf 当这个节点是一个叶子结点时为真.val 变量储存叶子结点所代表的区域的值. 你的任务是使用一个四叉树表示给定的网络.下面的例子将有助于你理解这个问题: 给定下面这个8 x 8 网络,我们将这样建立一个对应的四叉树: 由上…

建立四叉树 我们想要使用一棵四叉树来储存一个 N x N 的布尔值网络.网络中每一格的值只会是真或假.树的根结点代表整个网络.对于每个结点, 它将被分等成四个孩子结点直到这个区域内的值都是相同的. 每个结点还有另外两个布尔变量: isLeaf 和 val.isLeaf 当这个节点是一个叶子结点时为真.val 变量储存叶子结点所代表的区域的值. 你的任务是使用一个四叉树表示给定的网络.下面的例子将有助于你理解这个问题: 给定下面这个8 x 8 网络,我们将这样建立一个对应的四叉树: 由上文的定义,…

Given two words (start and end), and a dictionary, find all shortest transformation sequence(s) from start to end, such that: Only one letter can be changed at a time    Each intermediate word must exist in the dictionary For example, Given:start = "…

Find all possible combinations of k numbers that add up to a number n, given that only numbers from 1 to 9 can be used and each combination should be a unique set of numbers. Ensure that numbers within the set are sorted in ascending order. Example 1…

Given a string S, you are allowed to convert it to a palindrome by adding characters in front of it. Find and return the shortest palindrome you can find by performing this transformation. For example: Given "aacecaaa", return "aaacecaaa&qu…

Given a 2D board and a list of words from the dictionary, find all words in the board. Each word must be constructed from letters of sequentially adjacent cell, where "adjacent" cells are those horizontally or vertically neighboring. The same le…

Design a data structure that supports the following two operations: void addWord(word)bool search(word) search(word) can search a literal word or a regular expression string containing only letters a-z or .. A . means it can represent any one letter.…

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 a pair: [0,1] Given the total number of courses and a l…

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 assume all four edges of the grid are all surrounded by…

Say you have an array for which the ith element is the price of a given stock on day i. Design an algorithm to find the maximum profit. You may complete at most k transactions. 解题思路: https://leetcode.com/discuss/18330/is-it-best-solution-with-o-n-o-1…