原题地址:http://oj.leetcode.com/problems/reorder-list/ 题意: Given a singly linked list L: L0→L1→…→Ln-1→Ln,reorder it to: L0→Ln→L1→Ln-1→L2→Ln-2→… You must do this in-place without altering the nodes' values. For example,Given {1,2,3,4}, reorder it to {1,4,…

问题的思路是这样: 循环取头部合并,事实上也能够换个角度来看,就是将后面的链表结点,一次隔空插入到第一部分的链表中. class Solution: # @param head, a ListNode # @return nothing def reorderList(self, head): if None == head or None == head.next: return head #找到中间点,截断 pfast = head pslow = head while pfast.next…

Given a singly linked list L: L0→L1→…→Ln-1→Ln, reorder it to: L0→Ln→L1→Ln-1→L2→Ln-2→… You must do this in-place without altering the nodes' values. For example, Given {1,2,3,4}, reorder it to {1,4,2,3}. 这道链表重排序问题可以拆分为以下三个小问题: 1. 使用快慢指针来找到链表的中点,并将链表从中…

题目来源 https://leetcode.com/problems/valid-palindrome/ Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases. For example,"A man, a plan, a canal: Panama" is a palindrome."race a car"…

题目来源 https://leetcode.com/problems/triangle/ Given a triangle, find the minimum path sum from top to bottom. Each step you may move to adjacent numbers on the row below. For example, given the following triangle [ [], [,4], [6,,7], [4,,8,3] ] The min…

题目来源 https://leetcode.com/problems/pascals-triangle-ii/ Given an index k, return the kth row of the Pascal's triangle. For example, given k = 3,Return [1,3,3,1]. 题意分析 Input:integer Output:kth row of the Pascal's triangle Conditions:只返回第n行 题目思路 同118,不…

题目来源 https://leetcode.com/problems/pascals-triangle/ Given numRows, generate the first numRows of Pascal's triangle. For example, given numRows = 5,Return [ [1], [1,1], [1,2,1], [1,3,3,1], [1,4,6,4,1] ] 题意分析 Input:integer Output:帕斯卡三角 Conditions:帕斯卡三…

题目来源 https://leetcode.com/problems/populating-next-right-pointers-in-each-node/ Given a binary tree struct TreeLinkNode { TreeLinkNode *left; TreeLinkNode *right; TreeLinkNode *next; } Populate each next pointer to point to its next right node. If th…

题目来源 https://leetcode.com/problems/flatten-binary-tree-to-linked-list/ Given a binary tree, flatten it to a linked list in-place. 题意分析 Input: binary tree Output: flattened tree Conditions:将一个二叉树压平为一个flatten 树,也就是一条斜线 题目思路 先将左右子树压平,然后将左子树嵌入到本节点与右子树之间.…

题目来源 https://leetcode.com/problems/path-sum-ii/ Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum. 题意分析 Input: a binary tree, sum Output: list of list. Conditions: 给定一个二叉树,将所有root-leaf的路径值和等于sum的路径返…

题目来源 https://leetcode.com/problems/path-sum/ 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. 题意分析 Input: a binary tree, sum Output: True or False Con…

题目来源 https://leetcode.com/problems/minimum-depth-of-binary-tree/ 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. 题意分析 Input: a binary tree…

题目来源 https://leetcode.com/problems/balanced-binary-tree/ Given a binary tree, determine if it is height-balanced. For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never d…

题目来源 https://leetcode.com/problems/binary-tree-level-order-traversal-ii/ Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root). 题意分析 Input: binary tree Output:…

题目来源 https://leetcode.com/problems/maximum-depth-of-binary-tree/ 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. 题意分析 Input: tree Output:…

题目来源 https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal/ Given a binary tree, return the zigzag level order traversal of its nodes' values. (ie, from left to right, then right to left for the next level and alternate between). 题意分…

题目来源 https://leetcode.com/problems/binary-tree-level-order-traversal/ Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level). 题意分析 Input: 一个二叉树 Output:一个每层数值组合的list Conditions:层次遍历 题目思路 采用…

题目来源 https://leetcode.com/problems/symmetric-tree/ Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center). 题意分析 Input:一个二叉树 Output:True or False Conditions: 判断一个二叉树是不是对称的 题目思路 一一对应判断值是否相等,注意要清楚谁对应谁. AC代码(Python)…

题目来源 https://leetcode.com/problems/same-tree/ 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. 题意分析 Input: twon bin…

题目来源 https://leetcode.com/problems/validate-binary-search-tree/ 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'…

题目来源 https://leetcode.com/problems/binary-tree-inorder-traversal/ iven a binary tree, return the inorder traversal of its nodes' values. For example:Given binary tree {1,#,2,3}, 1 \ 2 / 3 return [1,3,2]. 题意分析 Input:tree Output: inorder traversal Cond…

题目来源 https://leetcode.com/problems/restore-ip-addresses/ Given a string containing only digits, restore it by returning all possible valid IP address combinations. For example:Given "25525511135", return ["255.255.11.135", "255.25…

题目来源 https://leetcode.com/problems/reverse-linked-list-ii/ Reverse a linked list from position m to n. Do it in-place and in one-pass. For example:Given 1->2->3->4->5->NULL, m = 2 and n = 4, return 1->4->3->2->5->NULL. Note:G…

题目来源 https://leetcode.com/problems/decode-ways/ A message containing letters from A-Z is being encoded to numbers using the following mapping: 'A' -> 1 'B' -> 2 ... 'Z' -> 26 Given an encoded message containing digits, determine the total number…

题目来源 https://leetcode.com/problems/gray-code/ The gray code is a binary numeral system where two successive values differ in only one bit. Given a non-negative integer n representing the total number of bits in the code, print the sequence of gray co…

题目来源 https://leetcode.com/problems/merge-sorted-array/ Given two sorted integer arrays nums1 and nums2, merge nums2 into nums1 as one sorted array. Note:You may assume that nums1 has enough space (size that is greater or equal to m + n) to hold addit…

题目来源 https://leetcode.com/problems/word-search/ Given a 2D board and a word, find if the word exists in the grid. The word can be constructed from letters of sequentially adjacent cell, where "adjacent" cells are those horizontally or vertically…

题目来源 https://leetcode.com/problems/subsets-ii/ Given a collection of integers that might contain duplicates, nums, return all possible subsets. Note: Elements in a subset must be in non-descending order. The solution set must not contain duplicate su…

题目来源 https://leetcode.com/problems/subsets/ Given a set of distinct integers, nums, return all possible subsets. Note: Elements in a subset must be in non-descending order. The solution set must not contain duplicate subsets. 题意分析 Input: :type nums:…

题目来源 https://leetcode.com/problems/partition-list/ Given a linked list and a value x, partition it such that all nodes less than x come before nodes greater than or equal to x. You should preserve the original relative order of the nodes in each of t…