shulixu的博客

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 positi

问题描述：寻找字符串的最长回文子序列。Example 1:Input: "babad"Output: "bab"Note: "aba" is also a valid answer.Example 2:Input: "cbbd"Output: "bb"Soulution 1 （中心展开）：回文序列从中心字符向两边扩展两边元素相同，需要考虑奇数个和偶数个的情况。注意...

 Given a list of daily temperatures T, return a list such that, for each day in the input, tells you how many days you would have to wait until a warmer temperature. If there is no future day for wh...

Given a non-negative integer c, your task is to decide whether there're two integers a and b such that a2 + b2 = c.Example 1:Input: 5Output: TrueExplanation: 1 * 1 + 2 * 2 = 5 Example 2:...

Given an array of integers that is already sorted in ascending order, find two numbers such that they add up to a specific target number.The function twoSum should return indices of the two numbers ...

问题描述：两个有序数组，输出他们的中位数。The overall run time complexity should be O(log (m+n)).Example 1:nums1 = [1, 3]nums2 = [2]The median is 2.0Example 2:nums1 = [1, 2]nums2 = [3, 4]The median is (2 ...

##### 题目描述：Say you have an array for which the ith element is the price of a given stock on day i.Design an algorithm to find the maximum profit. You may complete as many transactions as you like ...

##### 题目描述：A robot is located at the top-left corner of a m x n grid (marked 'Start' in the diagram below).The robot can only move either down or right at any point in time. The robot is trying to...

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

题目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 poss

题目：Write a function to find the longest common prefix string amongst an array of strings.思路：先找到所有字符串最小长度，然后在这个范围内进行比较。每次从strs[0]中取一个char，和后面的字符串进行比较。public String longestCommonPrefix(String[]

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

You are given an n x n 2D matrix representing an image.Rotate the image by 90 degrees (clockwise).Note:You have to rotate the image in-place, which means you have to modify the input 2D matrix d

Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place.这道题难点在于不能用额外空间，直接根据是否为零的状态改变原矩阵会覆盖没有遍历到的矩阵数值。如果用额外空间的话就先判断一遍用新的相同大小的矩阵存储状态，再根据那个矩阵改变出初始矩阵的值。不能用额外空间的话

Write an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties:Integers in each row are sorted from left to right.The first integer of each

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 n

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]. 我的做法：用的是递归，定义doTraversa

There are two sorted arrays nums1 and nums2 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)).Example 1:nums1 = [1,

题目：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 become4 5 6 7 0 1 2).You are given a target value to search. If foun

##### 78. Subsets 求不含重复数字的数组的子集Given a set of distinct integers, nums, return all possible subsets (the power set).Note: The solution set must not contain duplicate subsets.Example:Input: num...

78 Permutation IGiven 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].和上次...

##### 题目描述：Say you have an array for which the ith element is the price of a given stock on day i.If you were only permitted to complete at most one transaction (i.e., buy one and sell one share o...

Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.Example:Input:[  1->4->5,  1->3->4,  2->6]Output: 1->1->2->3->4-...

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.An input string is valid if:Open brackets must be closed by the same type of b...

经过一个月的倦怠期，我徐汉三又回来啦！FLAG每天至少一道题坚持到秋招offer！！！今天的题目是DFS思想。https://leetcode.com/problems/surrounded-regions/Given a 2D board containing'X'and'O'(the letter O), capture all regions surrounded by'X...

题目要将相邻两个节点交换但是不能只交换数值。1. 我的方法 循环 1）需要注意判断是否是null，凡是要调用next就要注意了！ 2）注意交换两个节点之后，node指向的下一个并不是当前后面链表的头（因为后面也要交换），所以应该判断下后面会不会继续交换，如果是的话就要指向下下个，不然就直接指向下一个。class Solution { public ListNode ...

判断是否是回文链表，尽量在O（n）时间复杂度。思路：快慢指针，慢指针指向的前面一部分序列倒序（从后向前指）。当快指针到头时刚好慢指针把前一半倒序。此时Pre指针指向的是前面一般=半链表的倒叙的头， 慢指针指向后面一半的头。注意如果循环结束时快指针不是空则说明链表节点数是奇数个，那slow指针要向前移一个。还有循环判断条件应该是next 和next.next还有要先更改快指针，否...

要求不用乘除取余运算计算整形向零取整除法。Example 1:Input: dividend = 10, divisor = 3Output: 3Example 2:Input: dividend = 7, divisor = -3Output: -21. 不能超时，所以要用二分法来加速2. 边界条件。注意不要超过32位int的范围。特别恶心的：因为-2147483...

参考博主charlotte的总结，记录自己的刷题过程。她真的很棒~https://github.com/huxiaoman7/leetcodebookhttps://mp.weixin.qq.com/s?__biz=MzI0OTQwMTA5Ng==&mid=2247483819&idx=1&sn=071731261441f702f429ae9fc1b98b84&...

https://leetcode.com/problems/perfect-squares/Given a positive integer n, find the least number of perfect square numbers (for example, 1, 4, 9, 16, ...) which sum to n.Example 1:Input: n = 12...

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[ [2], [3,4], [6,5...

Given a positive integer n, break it into the sum of at least two positive integers and maximize the product of those integers. Return the maximum product you can get.Example 1:Input: 2Output: 1...

##### 题目描述：Given a non-negative index k where k ≤ 33, return the kth index row of the Pascal's triangle.Note that the row index starts from 0.Example:Input: 3Output: [1,3,3,1]##### 分析：...

Given an array of strings, group anagrams together.Example:Input: ["eat", "tea", "tan", "ate", "nat", "bat"],Output:[ ["ate","eat","tea"], ["nat"

Given a non-empty string s and a dictionary wordDict containing a list of non-empty words, determine if s can be segmented into a space-separated sequence of one or more dictionary words.Note:The ...

96. Unique Binary Search TreesGiven n, how many structurally unique BST's (binary search trees) that store values 1 ... n?Example:Input: 3Output: 5Explanation:Given n = 3, there are a total ...

39. Combination SumGiven a set of candidate numbers (candidates) (without duplicates) and a target number (target), find all unique combinations in candidates where the candidate numbers sums to tar...

22. Generate ParenthesesGiven n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.For example, given n = 3, a solution set is:[ "((()))", "(()()...

Given two words word1 and word2, find the minimum number of operations required to convert word1 to word2.You have the following 3 operations permitted on a word:Insert a character Delete a chara...

17. Letter Combinations of a Phone NumberGiven a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent.A mapping of digit to letters ...