中华胡杨的专栏

问题描述： Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.For example, Given the following matrix:[ [ 1, 2, 3 ], [ 4, 5, 6 ], [ 7, 8, 9 ] ]

问题描述： 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.这道题注意什么是叶子节点就好，即左右节点均为空。代码如下：/** *

Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place.click to show follow up.Follow up:Did you use extra space?A straight forward solution using O(m

问题描述： Given an array of strings, return all groups of strings that are anagrams.Note: All inputs will be in lower-case.首先，先明白什么叫anagrams，比如eat\ate\tea，这三种，字符一样，但是顺序不同，就叫anagrams。代码如下： public Array

问题描述： 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 do

问题描述： 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?这道题如果单纯使用DFS的话会超时，比较好的方法是存一个数组

问题描述： 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 s

问题描述： Implement strStr().Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.可能唯一需要注意的是，如果部分满足字符串的要求时，需要将指针回拨到开始满足匹配的下一个再进行。代码如下：运行时间（0ms)int strSt

问题描述： 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 add

问题描述： 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:“((()))”, “(()())”, “(())()”, “()(())”, “()()()

问题描述： Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.For example, Given n = 3,You should return the following matrix: [ [ 1, 2, 3 ], [ 8, 9, 4 ],

问题描述： Reverse digits of an integer.Example1: x = 123, return 321 Example2: x = -123, return -321这道题比较讨厌的地方在于如何判断溢出，好吧，我的方法比较low，因为我只会比较+法的溢出，，但是效果还不错，运行时间是4msint reverse(int x) { bool negative =

题目描述：Given an array of integers, find out whether there are two distinct indices i and j in the array such that the difference between nums[i] and nums[j] is at most t and the difference between

问题描述： Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.Note: Elements in a triplet (a,b,c) mu

问题描述： Given a digit string, return all possible letter combinations that the number could represent.A mapping of digit to letters (just like on the telephone buttons) is given below. Input:Digit stri

问题描述： 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,

问题描述 Find the contiguous subarray within an array (containing at least one number) which has the largest sum.For example, given the array [−2,1,−3,4,−1,2,1,−5,4], the contiguous subarray [4,−1,2,

问题描述： Given an integer, write a function to determine if it is a power of two.解析：这道题问的是是不是2的指数，而不是是不是有个数的平方，，bool isPowerOfTwo(int n) { if(n<=0) return false; if(n&(n-1)) retur

问题描述： 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 e

问题描述： Given a roman numeral, convert it to an integer.Input is guaranteed to be within the range from 1 to 3999.代码分析：罗马数字转换成整数的规则如下：如果前一个数的值小于后一个数的值，那么这个数为后者减去前者。如果前者大于后者，那么就是简单地相加即可。代码如下：28msint getV

问题描述： Validate if a given string is numeric.Some examples: “0” => true ” 0.1 ” => true “abc” => false “1 a” => false “2e10” => true Note: It is intended for the problem statement to be ambiguous

问题描述： Given n non-negative integers a1, a2, …, an, where each represents a point at coordinate (i, ai). n vertical lines are drawn such that the two endpoints of line i is at (i, ai) and (i, 0). Find

问题描述： 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 du

问题描述： Given an array and a value, remove all instances of that value in place and return the new length.The order of elements can be changed. It doesn’t matter what you leave beyond the new length.代码如

问题描述： Implement a basic calculator to evaluate a simple expression string.The expression string may contain open ( and closing parentheses ), the plus + or minus sign -, non-negative integers and empt

问题描述： Given a sorted array, remove the duplicates in place such that each element appear only once and return the new length.Do not allocate extra space for another array, you must do this in place wi

问题描述： Divide two integers without using multiplication, division and mod operator.If it is overflow, return MAX_INT.分析：这道题不允许用*/和%运算，因此只能模拟计算机对乘除法的做法来进行。请参考另外一篇博客：这里写链接内容另外，这道题最恶心的是一些边界值。如被除数为-2147483

问题描述： 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: Elements in

问题描述： Given an integer n, return the number of trailing zeroes in n!.Note: Your solution should be in logarithmic time complexity.Credits: Special thanks to @ts for adding this problem and creating a

问题描述：原题链接分析：我之前做过这道题，但是无意间看到网上的一种做法，实在是拍案叫绝，爱不释手，第一个发明这个解法的大神，请收下我的膝盖。 这道题很明显是用栈的结构，但是这里面有几个小问题，就是怎么确定柱的边界。这里是指左右延伸的边界，我的做法太丑就不赘述了，它的做法是维护一个栈，一个高度值从低到高的栈（而且维护的是索引）。那么当某个元素要出栈时，那么高度自然就是该元素本身的高度。 那么讨论宽

问题描述：原文链接分析：这道题其实比较简单，主要思想是维护两个链表，一个比x小的链表，一个大的链表，最后这两个链表结合起来，时间复杂度为Ｏ（ｎ），空间复杂度为Ｏ（１）。代码如下：４ｍｓ/** * Definition for singly-linked list. * struct ListNode { * int val; * struct ListNode *next;

原题链接分析：这道题反正我是想不出来，直接看的网友的解题思路，核心思想是将矩阵中1的个数转化成直方图，而直方图在leetcode-84中已经有了解题方案。怎么想到这个方法的，不知道，，， 如何将其转化为直方图？初始元素为0，对每一行，每一列中的每一个元素，如果为1，height[j]++，如果为0，height[j]为0；，这样对于每一行，都找到了最大值。代码如下：28msclass Soluti

问题描述： Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a BST.Calling next() will return the next smallest number in the BST.Note: next() a

问题描述： 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: You may assum

问题如下： 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

问题描述： Given a linked list, reverse the nodes of a linked list k at a time and return its modified list.If the number of nodes is not a multiple of k then left-out nodes in the end should remain as it

问题描述： Write a function to delete a node (except the tail) in a singly linked list, given only access to that node.Supposed the linked list is 1 -> 2 -> 3 -> 4 and you are given the third node with val

问题描述：原文链接分析：这道题其实就是找规律，有两种思路，分别见：方法1、方法2 我个人觉得方法2会更好，首先，它是根据二进制转的格雷码，操作起来更方便一些。class Solution {public: vector<int> grayCode(int n) { int size = 1<<n;//nums of the total; vector<in

问题描述： Given an array of numbers nums, in which exactly two elements appear only once and all the other elements appear exactly twice. Find the two elements that appear only once.For example:Given nums

问题描述： Given a binary tree, return all root-to-leaf paths.For example, given the following binary tree:1 / \ 2 3 \ 5 All root-to-leaf paths are:[“1->2->5”, “1->3”]分析：使用递归的思想，且递归到叶节点时终止，即