teffi的专栏

描述 Implement pow(x, n).分析 二分法，xn = xn/2 × xn/2 × xn%2代码class Solution {public: double myPow(double x, int n) { if (n < 0) return 1.0 / power(x, -n); else return power(x, n);

描述 Given an integer (signed 32 bits), write a function to check whether it is a power of 4.Example: Given num = 16, return true. Given num = 5, return false.Follow up: Could you solve it without loop

描述 Given an integer, write a function to determine if it is a power of two.分析 如果是power of two, 则2进制表达中,有且仅有一个1. 可以通过移位来数1的个数, 这里用了一个巧妙的办法, 即判断 N & (N-1) 是否为0. 代码class Solution {public: bool i

描述 Given an array with n objects colored red, white or blue, sort them so that objects of the same color are adjacent, with the colors in the order red, white and blue.Here, we will use the integers 0

描述 Given a string, find the first non-repeating character in it and return it’s index. If it doesn’t exist, return -1.Examples:s = "leetcode"return 0.s = "loveleetcode",return 2.Note: You may assume

描述 Given an unsorted integer array, find the first missing positive integer.For example, Given [1,2,0] return 3, and [3,4,-1,1] return 2.Your algorithm should run in O(n) time and uses constant spac

描述 Given an array S of n integers, are there elements a, b, c, and d in S such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.Note: The solution se

描述 Given an array S of n integers, find three integers in S such that the sum is closest to a given number, target. Return the sum of the three integers. You may assume that each input would have exac

描述 Write a function that takes a string as input and returns the string reversed.Example: Given s = “hello”, return “olleh”.分析 翻转字符串。 取字符串长度的一半进行循环，首尾交换。代码class Solution {public: string revers

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: A word is define

描述 Given two binary strings, return their sum (also a binary string).For example, a = “11” b = “1” Return “100”.分析 翻转a和b，逐位相加求值，结果存入string中。 注意最高位的情况。代码class Solution {public: string addBina

描述 Given an integer, convert it to a roman numeral.Input is guaranteed to be within the range from 1 to 3999.分析 整数转换为罗马数字。 此题因为题目中明确了范围1到3999，所以用每位对应一个数组的方式较为简单。附罗马数字的规则：罗马数字共有7个，即I（1）、V（5）、X（10）、L（

描述 Given a roman numeral, convert it to an integer.Input is guaranteed to be within the range from 1 to 3999.分析 罗马数字转换为整数。附罗马数字的规则：罗马数字共有7个，即I（1）、V（5）、X（10）、L（50）、C（100）、D（500）和M（1000）。 1、重复数次：一个罗马数

描述 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” is not a p

描述 You are given an n x n 2D matrix representing an image.Rotate the image by 90 degrees (clockwise).Follow up: Could you do this in-place?分析 首先想到，纯模拟，从外到内一圈一圈的转，但这个方法太慢。 如下图，首先沿着副对角线翻转一次，然后沿着水平中

描述 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” “

描述 Given a collection of distinct 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], [3,2,1]]分析

描述 Implement next permutation, which rearranges numbers into the lexicographically next greater permutation of numbers.If such arrangement is not possible, it must rearrange it as the lowest possible

描述You are climbing a stair case. It takes n steps to reach to the top.Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?Note: Given n will be a positive in

描述 Suppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand.(i.e., 0 1 2 4 5 6 7 might become 4 5 6 7 0 1 2).You are given a target value to search. If found in th

描述Follow up for "Search in Rotated Sorted Array":What if duplicates are allowed?Would this affect the run-time complexity? How and why?Suppose an array sorted in ascending order is rotated at some piv

描述 Given an unsorted array of integers, find the length of the longest consecutive elements sequence.For example, Given [100, 4, 200, 1, 3, 2], The longest consecutive elements sequence is [1, 2, 3,

题目： Given an array of integers, return indices of the two numbers such that they add up to a specific target.You may assume that each input would have exactly one solution.Example:Given nums = [2, 7,

Given a binary array, find the maximum number of consecutive 1s in this array.Example 1:Input: [1,1,0,1,1,1]Output: 3Explanation: The first two digits or the last three digits are consecutive 1s.

The string “PAYPALISHIRING” is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility) P A H NA P L S I I G

Determine whether an integer is a palindrome. Do this without extra space.分析： 1. 如果将数字转化为字符串，再判断是否为回文字符串，要使用额外空间，不满足要求。 2. 考虑将数字翻转，(LeetCode 7. Reverse Integer )[http://blog.youkuaiyun.com/teffi/article/d

Implement atoi to convert a string to an integer.Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input cases.N

Reverse digits of an integer.Example1: x = 123, return 321 Example2: x = -123, return -321分析：注意溢出情况。class Solution {public: int reverse(int x) { int digit = 0; int sign = 1;

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 linked list.

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 solution is trivial, could y

Given a root node reference of a BST and a key, delete the node with the given key in the BST. Return the root node reference (possibly updated) of the BST.Basically, the deletion can be divided into t

Given a binary tree, return the inorder traversal of its nodes’ values.For example: Given binary tree [1,null,2,3], 1 \ 2 / 3return [1,3,2].Note: Recursive solution is trivial, could

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 solution is trivial, could

You are given a binary tree in which each node contains an integer value.Find the number of paths that sum to a given value.The path does not need to start or end at the root or a leaf, but it must go

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 search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two

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, find the lowest common ancestor (LCA) of two given nodes in the tree.According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes v and

Find the sum of all left leaves in a given binary tree.Example: 3 / \ 9 20 / \ 15 7There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.LeetCod

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"]LeetCode AC代码：/** * Definition