Coding for Dreams

这题很简单，但还是超时和WA一次主要是由于1、这题输入可能是非常大的数，可能上千位，所以把输入当成了2000位的字符串来处理，转化成数字2、还是变量初始化的问题，WA了一个，细心最重要#include #include using namespace std;int f (int n){ int sum = 0; while((n/10) > 0){ sum +=

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", "255.255.111.35"]. (Order does not m

Given a collection of numbers, return all possible permutations.For example,[1,2,3] have the following permutations:[1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], and [3,2,1].思路分析：这题是Permutations II问题的简

题目 Given a collection of numbers that might contain duplicates, return all possible unique permutations.For example,[1,1,2] have the following unique permutations:[1,1,2], [1,2,1], and [2,1,1].思路分析：Pe

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 nei

Given a collection of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.Each number in C may only be used once in the combination.N

Given a set of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.The same repeated number may be chosen from C unlimited number of

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.思路分析：判断两个树是否相同，基本也

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.思路分析：这题比较简单，关于树的题目通常都可以用递归解决，这题也不例外，递归解法的思

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.思路分析:这题和Maximum Depth of Binary Tree类似，但是现

The set [1,2,3,…,n] contains a total of n! unique permutations.By listing and labeling all of the permutations in order,We get the following sequence (ie, for n = 3):"123""132""213""231""312""321"Give

这是最近比较火的一个题目，因为一条推特的转播“Google HR：我们90%的工程师都用你写的软件，但是你竟然不会在白板上面反转一颗二叉树，所以滚吧”，各方看法不一，但看这个题目，的确是一个很简单的题目。考察最基本的递归和树操作。下面给出了递归实现和借助栈的迭代实现（非递归实现）。后一个版本的可扩展性更好，可以处理更大的树。实在是容易题，就是DFS遍历一遍树节点，把每个树节点的左右孩子互换就可以了。或许是那个ios开发牛人不屑于准备就去Google面试，结果被爆，与其说是能力问题，不如说是态度问题。

There are two sorted arrays A and B of size m and n respectively. Find the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)).思路分析：这题容易想到O(m+n)的解法，就是先Merge两个数组，然后返

Given a string s and a dictionary of words dict, add spaces in s to construct a sentence where each word is a valid dictionary word.Return all such possible sentences.For example, given s = “catsanddo

这题主要求二叉树结点到根结点的路径长度，基本的思路是 比较a与b，如果a大则当前结点是左孩子，a-b作为父结点的左数，父结点的右数与当前右数相等；如果b大则当前结点为右孩子，同理可以求父结点，直到父结点为（1，1）遍历结束。当用原始的递归算法会超时，需要考虑a=1或b=1的特殊情况，同时利用a与b的倍数关系加快遍历速度Source CodeProblem: 2499

通过分类讨论，将规模较大的问题转换成规模较小的相同问题，学会”降维“，将索引值不断降小，就可以递归求解设f(m,n)为把m个苹果放到n个盘子中的方法数，m>=0,n>=0.若m和n中任何一个等于0，那么f(m,n) = 1，注意不是等于0，因为相当于就那么一种结果，就是不往盘子里面放（没有苹果），或者，连盘子都没有。若n=1,显然对于任意的m>=0 有f(m,1) = 1若m=

//全排列问题，近期面试的热门考题，收录于此/* 设R={r1,r2,...rn}是要进行排列的n个元素.Ri=R-{ri}.集合X中元素的全排列记为 Perm(X).(ri)Perm(X)表示在全排列Perm(X)的每一个排列前加上前缀ri得到的排列 R的全排列可归纳定义如下: 当n=1时,Perm(R)=(r),其中r是集合R中唯一的元素;

LeetCode Validate Binary Search TreeGiven 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

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.For example, given n = 3, a solution set is:"((()))", "(()())", "(())()", "()(())", "()()()"思路分析：

Sort a linked list in O(n log n) time using constant space complexity.思路分析：这题要求在O(n log n) 和常量空间对单链表排序，O(n log n) 的排序算法有快速排序，归并排序和堆排序，对于快速排序，其最坏情况下的时间复杂读是O（n），所以不符合要求。我们可以用归并排序解决这题。用归并排序的好处是平均时间和最坏时间都

Given inorder and postorder traversal of a tree, construct the binary tree.思路分析：这题主要考察递归，我们可以画一个二叉树的实例来具体分析。比如如果postorder 是84526731，inorder是84521637，首先我们可以知道postorder的最后一个数1必然是root，然后我们可以在inorder里面找到这

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 / \

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 = 22

Given preorder and inorder traversal of a tree, construct the binary tree.Note:You may assume that duplicates do not exist in the tree.思路分析：这题类似于LeetCode Construct Binary Tree from Inorder and Postord

Given a binary search tree, write a function kthSmallest to find the kth smallest element in it.Note: You may assume k is always valid, 1 ≤ k ≤ BST's total elements.Follow up:What if the BST is modifi