flyljg的专栏

Implement int sqrt(int x).Compute and return the square root of x.1. 二分法：用unsigned long long。最后返回值还要再检查一下。class Solution {public: int mySqrt(int x) { unsigned long long be

题目描述：找出只是出现一次的数字，其他的数字都出现两次。思路：根据x^x=0,x^y=y^x。只要将所有数异或就完成了。代码实现：class Solution{public: int singleNumber(vector &nums){ int x=0; for(int i=0;i<nums.size();i++){

题目描述：Given a string s consists of upper/lower-case alphabets and empty space characters ' ', return the length of last word in the string.If the last word does not exist, return 0.Note

题目描述：Given two strings s and t, write a function to determine if t is an anagram of s.For example,s = "anagram", t = "nagaram", return true.s = "rat", t = "car", return false.Note:

题目描述:Invert a binary tree. 4 / \ 2 7 / \ / \1 3 6 9to 4 / \ 7 2 / \ / \9 6 3 1Trivia:This problem was inspired by this original tweet by

You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a link

Given a linked list, remove the nth node from the end of list and return its head.For example, Given linked list: 1->2->3->4->5, and n = 2. After removing the second node from the end, the

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 diffe

Given a sorted linked list, delete all duplicates such that each element appear only once.For example,Given 1->1->2, return 1->2.Given 1->1->2->3->3, return 1->2->3.思路：算法没什么好说的，链表实现一个功能：

Given a binary tree, find the maximum path sum.The path may start and end at any node in the tree.For example:Given the below binary tree, 1 / \ 2 3Return 6.

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

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.题目描述：             求二叉树的最小深度。和求

Given a non-negative integer num, repeatedly add all its digits until the result has only one digit.For example:Given num = 38, the process is like: 3 + 8 = 11, 1 + 1 = 2. Since 2 has on

Related to question Excel Sheet Column TitleGiven a column title as appear in an Excel sheet, return its corresponding column number.For example: A -> 1 B -> 2 C -> 3 ...

Given a positive integer, return its corresponding column title as appear in an Excel sheet.For example: 1 -> A 2 -> B 3 -> C ... 26 -> Z 27 -> AA 28 -> AB Credits

题目描述：给定一个完全二叉树，找到每个节点在这一层右边的点。思路：直接DFS。将每个点左儿子向右全部指向右儿子向左上对应的节点。代码实现：/** * Definition for binary tree with next pointer. * struct TreeLinkNode { * int val; * TreeLinkNode *left

问题描述：这是算法中比较经典的问题，判断一个字符串是否是另一个字符串的字串。思路：这个题目最经典的算法应该是KMP算法，KMP算法是最优的线性算法，复杂度已经达到了这个问题的下线。但是KMP算法的过程比较复杂，在面试过程中很难在很短的时间内实现，所以在一般的面试中很少让实现KMP算法。代码实现：class Solution {public: int strSt

问题描述：逆波兰表达式求值，经典问题。思路：遇到数字入栈，遇到符号取栈顶的两个元素出来，再将结果入栈，最后栈里剩下的元素就是结果了。实现代码：class Solution {public: int evalRPN(vector& tokens) { stack st; for(auto &s:tokens){

Given n points on a 2D plane, find the maximum number of points that lie on the same straight line.分析：任意一条直线都可以表述为y = ax + b假设，有两个点(x1,y1), (x2,y2)，如果他们都在这条直线上则有y1 = kx1 +b

Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and set.get(key) - Get the value (will always be positive) of the key if

Given a binary tree, return the preorder traversal of its nodes' values.For example:Given binary tree {1,#,2,3}, 1 \ 2 / 3return [1,2,3].Note: Recursive soluti

Given a binary tree, return the preorder traversal of its nodes' values.For example:Given binary tree {1,#,2,3}, 1 \ 2 / 3return [1,2,3].Note: Recursive soluti

Given a binary tree, return the inorder traversal of its nodes' values.For example:Given binary tree {1,#,2,3}, 1 \ 2 / 3return [1,3,2].Note: Recursive solutio

题目描述：Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.The brackets must close in the correct order, "()" and "()[]{}" are

题目描述：给定一个有序数组，数组元素升序排列，将该有序数组转换为一个平衡二叉搜索树。思路：首先，这个问题很容易用递归方法来解决。所谓的平衡的定义：就是二叉树的子树高度之差不能超过1。如果要从一个有序数组中选择一个元素作为根节点，首先应该用二分查找算法，对数组进行均匀换分，然后将有序数组的中间元素作为根节点。选择中间元素作为根节点并创建之后，剩下的元素分为两部分，可以看做是两个数组，

题目描述：从根到叶子的每条路径构成一个数，求这些数的和。思路：直接DFS，每次到叶子加就可以了。代码实现：/** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; *

Given a binary tree, return the postorder traversal of its nodes' values.For example:Given binary tree {1,#,2,3}, 1 \ 2 / 3return [3,2,1].Note: Recursive solut

题目描述：判断一个字符串是否是回文串。注意只有大小写字母和数字才算是串的内容，其他字符都跳过。思路：左右两个指针逐渐往中间逼近就可以了。isalnum（）函数是判断是否是字母数字的，其他字符跳过；tolower（）函数是将字母数字都转换成小写进行判断。算法实现：class Solution{public: bool isPalindrome(str

题目描述：求树上有没有从根节点到叶子的路节点的值加起来为N。思路：DFS。到叶子判断累加值是否等于SUM。代码实现：/** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right

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：递归求解二叉树的深度，左右子树较深的+1（；解释主要原

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.题目描述： 

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

Given an array nums, write a function to move all 0's to the end of it while maintaining the relative order of the non-zero elements.For example, given nums = [0, 1, 0, 3, 12], after calling you