墨染百城

收集在刷LeetCode过程中遇到的经典代码，持续更新。136. Single Number中使用异或求解问题描述问题链接：https://leetcode.com/problems/single-number/#/descriptionGiven an array of integers, every element appears twice except for one. Find that

昨天开始刷LeetCode，在这个过程中学到了不少Trick，为了方便复习，特地整理出来。List转String[]示例代码：List<String> wordList = new ArrayList<String>();String[] results = new String[wordList.size()];wordList.toArray(results);获得char在String中

问题描述问题链接：https://leetcode.com/problems/next-greater-element-i/#/descriptionYou are given two arrays (without duplicates) nums1 and nums2 where nums1’s elements are subset of nums2. Find all the next gr

问题描述问题链接：https://leetcode.com/problems/reverse-string/#/descriptionWrite a function that takes a string as input and returns the string reversed.Example:Given s = "hello", return "olleh".我的代码探索过程这么简单的

问题描述问题链接：https://leetcode.com/problems/fizz-buzz/#/descriptionWrite a program that outputs the string representation of numbers from 1 to n.But for multiples of three it should output “Fizz” instead of

问题描述问题链接：https://leetcode.com/problems/best-time-to-buy-and-sell-stock/#/descriptionSay 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

一直很想学习动态规划算法，虽然也在课上听老师讲过背包问题啊，旅行商问题啊，但是都是懵懵懂懂的匆匆而过，一直也没有学会。这次刷LeetCode也给了我一个机会来弥补之前的遗憾。参考资料http://blog.youkuaiyun.com/baidu_28312631/article/details/47418773http://www.hawstein.com/posts/dp-novice-to-advance

问题描述问题链接：https://leetcode.com/problems/counting-bits/#/descriptionGiven a non negative integer number num. For every numbers i in the range 0 ≤ i ≤ num calculate the number of 1’s in their binary repre

问题描述问题链接：https://leetcode.com/problems/battleships-in-a-board/#/descriptionGiven an 2D board, count how many battleships are in it. The battleships are represented with ‘X’s, empty slots are represente

问题描述问题链接：https://leetcode.com/problems/island-perimeter/#/descriptionYou are given a map in form of a two-dimensional integer grid where 1 represents land and 0 represents water. Grid cells are connect

问题描述问题链接：https://leetcode.com/problems/max-consecutive-ones/#/descriptionGiven a binary array, find the maximum number of consecutive 1s in this array.Example 1:Input: [1,1,0,1,1,1]Output: 3Explanati

问题描述问题链接：https://leetcode.com/problems/maximum-subarray/#/descriptionFind the contiguous subarray within an array (containing at least one number) which has the largest sum.For example, given the array

问题描述问题链接：https://leetcode.com/problems/single-number/#/descriptionGiven a word, you need to judge whether the usage of capitals in it is right or not.We define the usage of capitals in a word to be rig

问题描述问题链接：https://leetcode.com/problems/single-number/#/descriptionGiven an array of integers, every element appears twice except for one. Find that single one.Note:Your algorithm should have a linear r

问题描述问题链接：https://leetcode.com/problems/arithmetic-slices/#/descriptionA sequence of number is called arithmetic if it consists of at least three elements and if the difference between any two consecuti

问题描述问题链接：https://leetcode.com/problems/add-digits/#/descriptionGiven a non-negative integer num, repeatedly add all its digits until the result has only one digit.For example:Given num = 38, the proces

问题描述问题链接：https://leetcode.com/problems/queue-reconstruction-by-height/#/descriptionSuppose you have a random list of people standing in a queue. Each person is described by a pair of integers (h, k), w

问题描述问题链接：https://leetcode.com/problems/find-bottom-left-tree-value/#/descriptionGiven a binary tree, find the leftmost value in the last row of the tree.Example 1:Input: 2 / \ 1 3Output:1Ex

问题描述问题链接：https://leetcode.com/problems/nim-game/#/descriptionYou are playing the following Nim Game with your friend: There is a heap of stones on the table, each time one of you take turns to remove 1

问题描述问题链接：https://leetcode.com/problems/keyboard-row/#/descriptionGiven a List of words, return the words that can be typed using letters of alphabet on only one row’s of American keyboard like the imag

问题描述问题链接：https://leetcode.com/problems/number-complement/#/descriptionGiven a positive integer, output its complement number. The complement strategy is to flip the bits of its binary representation.No

问题描述问题链接：https://leetcode.com/problems/hamming-distance/#/descriptionThe Hamming distance between two integers is the number of positions at which the corresponding bits are different.Given two integer

问题描述问题链接：https://leetcode.com/problems/invert-binary-tree/#/descriptionInvert a binary tree. 4 / \ 2 7 / \ / \1 3 6 9to 4 / \ 7 2 / \ / \9 6 3 1Trivia:

问题描述问题链接：https://leetcode.com/problems/sum-of-two-integers/#/descriptionCalculate the sum of two integers a and b, but you are not allowed to use the operator + and -。Example:Given a = 1 and b = 2, ret

问题描述问题链接：https://leetcode.com/problems/convert-bst-to-greater-tree/#/descriptionGiven a Binary Search Tree (BST), convert it to a Greater Tree such that every key of the original BST is changed to the

问题描述问题链接：https://leetcode.com/problems/binary-watch/#/descriptionGiven an array of integers, 1 ≤ a[i] ≤ n (n = size of array), some elements appear twice and others appear once.Find all the elements th

问题描述问题链接：https://leetcode.com/problems/count-numbers-with-unique-digits/#/descriptionGiven a non-negative integer n, count all numbers with unique digits, x, where 0 ≤ x < 10n.Example:Given n = 2, retu

问题描述问题链接：https://leetcode.com/problems/binary-watch/#/descriptionA binary watch has 4 LEDs on the top which represent the hours (0-11), and the 6 LEDs on the bottom represent the minutes (0-59).Each LE

问题描述问题链接：https://leetcode.com/problems/beautiful-arrangement/#/descriptionSuppose you have N integers from 1 to N. We define a beautiful arrangement as an array that is constructed by these N numbers s

问题描述问题链接：https://leetcode.com/problems/find-all-numbers-disappeared-in-an-array/#/descriptionGiven an array of integers where 1 ≤ a[i] ≤ n (n = size of array), some elements appear twice and others app

问题描述问题链接：https://leetcode.com/problems/minesweeper/#/descriptionLet’s play the minesweeper game (Wikipedia, online game)!You are given a 2D char matrix representing the game board. ‘M’ represents an un

问题描述问题链接：https://leetcode.com/problems/most-frequent-subtree-sum/#/descriptionGiven the root of a tree, you are asked to find the most frequent subtree sum. The subtree sum of a node is defined as the

这几天陆续听说同学们都在刷LeetCode，是面试必须的。听完我也坐不住了，决定开始刷起来。先在知乎看了一遍，大部分人都是按照AC rate从高到低刷，那么我也就这么办吧。同学还建议直接在网页上写代码，这样可以适应在线笔试时的手写要求。稍后把解决方案放到GitHub上去。问题描述问题连接：https://leetcode.com/problems/encode-and-decode-tinyurl/

问题描述问题链接：https://leetcode.com/problems/minimum-moves-to-equal-array-elements-ii/#/descriptionGiven a non-empty integer array, find the minimum number of moves required to make all array elements equal,

之前刚刚实现了快速排序算法。现在还有一个要求就是找到一个序列中第K大的数。我们当然可以用先排序再取值的方法来做，这样的时间复杂度为O(NlogN)。或者使用heap_sort，或者优先队列，则复杂度是O(NlogK)。那么有没有一种更加高效的方式呢？答案是肯定的。可以使用快速排序的一个变种quick_select，则平均复杂度为O(N)，最坏复杂度为O(N^2)。算法思想通过一趟快排过后，序列将被分

参考资料http://www.cnblogs.com/steven_oyj/archive/2010/05/22/1741376.html概念回溯算法实际上一个类似枚举的搜索尝试过程，主要是在搜索尝试过程中寻找问题的解，当发现已不满足求解条件时，就“回溯”返回，尝试别的路径。回溯法是一种选优搜索法，按选优条件向前搜索，以达到目标。但当探索到某一步时，发现原先选择并不优或达不到目标，就退回一步重新选择

今天刷题的时候要用到快排，然后发现居然写不出来了，好沮丧啊。看来基础知识还需要好好加强，先把快排补起来。简介快速排序由C. A. R. Hoare在1962年提出。它的基本思想是：通过一趟排序将要排序的数据分割成独立的两部分，其中一部分的所有数据都比另外一部分的所有数据都要小，然后再按此方法对这两部分数据分别进行快速排序，整个排序过程可以递归进行，以此达到整个数据变成有序序列。算法步骤设要排序的数组

问题描述问题链接：https://leetcode.com/problems/find-the-difference/#/descriptionGiven two strings s and t which consist of only lowercase letters.String t is generated by random shuffling string s and then add

问题描述问题链接：https://leetcode.com/problems/teemo-attacking/#/descriptionIn LLP world, there is a hero called Teemo and his attacking can make his enemy Ashe be in poisoned condition. Now, given the Teemo’s

问题描述问题链接：https://leetcode.com/problems/maximum-depth-of-binary-tree/#/descriptionGiven a binary tree, find its maximum depth.The maximum depth is the number of nodes along the longest path from the roo