Problem link: http://oj.leetcode.com/problems/single-number-ii/ The problem seems like the Single Number. Suppose we have following (3m+1) numbers in the array A: x0, x1, x1, x1, ..., xm, xm, xm We are asked to find out the value of x0. However we ca…

Prolbem link: http://oj.leetcode.com/problems/single-number/ This prolbem can be solved by using XOR(exclusive OR) operation. Let x, y, and z be any numbers, and XOR has following properties: x XOR 0 is itself, i.e. x XOR 0 = 0; x XOR x is 0, i.e. x…

Problem Link: http://oj.leetcode.com/problems/path-sum-ii/ The basic idea here is same to that of Path Sum. However, since the problem is asking for all possible root-to-leaf paths, so we should use BFS but not DFS. The python code is as follows. # D…

Problem Link: http://oj.leetcode.com/problems/word-ladder-ii/ Basically, this problem is same to Word Ladder I, which uses a double-direction BFS. However, the difference is that we need to keep track of all paths during the double-direction BFS in o…

Problem Link: http://oj.leetcode.com/problems/palindrome-partitioning-ii/ We solve this problem by using Dynamic Programming. Optimal Sub-structure Assume a string S has the palindrome minimum cuts n, and S = W1 + W2 + ... + Wn where Wi is a palindro…

Problem link: http://oj.leetcode.com/problems/word-break-ii/ This problem is some extension of the word break problem, so the solution is based on the discussion in Word Break. We also use DP to solve the problem. In this solution, A[i] is not a bool…

问题描述:给出一个整数数组,除了一个元素外,其他每个元素都出现了2次,找出只出现1次的元素. int singleNumber(vector<int>& nums); 分析:比较自然的想法是用一个容器来进行插入.查找.删除操作.遍历nums,先查找容器中是否包含该元素,是则插入,否则删除.最后容器中只剩下只出现1次的元素. 解法: int singleNumber(vector<int>& nums) { int i = 0; unordered_set<in…

Given an array of integers, every element appears three times except for one. Find that single one. Note:Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory? 思路: 这个题是Single Number的进阶版,如果其他的数都出现两次而…

题目描述: 给定一个数组,里面除了一个数字,其他的都出现三次.求出这个数字 原文描述: Given an array of integers, every element appears three times except for one. Find that single one. Note: Your algorithm should have a linear runtime complexity. Could you implement it without using extra m…

Given an integer array of size n, find all elements that appear more than ⌊ n/3 ⌋ times. The algorithm should run in linear time and in O(1) space. 思路: [LeetCode 169]Majority Element 的拓展,这回要求的是出现次数超过三分之一次的数字咯,动动我们的大脑思考下,这样的数最多会存在几个呢,当然是2个嘛.因此,接着上一题的方…

Problem Discription: Suppose the array A has n items in which all of the numbers apear 3 times except one. Find the single number. int singleNumber2(int A[], int n) { ; while(n--) { ret ^= A[n]; } return ret; } Related Problem: Suppose the array A ha…

Given an array of integers, every element appears three times except for one. Find that single one. Note:Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory? 解题思路: 在 Single Number I 中使用了异或一个数两次,原值…

Given an array of integers, every element appears three times except for one. Find that single one. Note:Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory? 没辙,智商碾压题.楼主没遇到之前就只会这种做法. public int si…

Problem Link: http://oj.leetcode.com/problems/interleaving-string/ Given s1, s2, s3, find whether s3 is formed by the interleaving of s1 and s2. For example, Given: s1 = "aabcc", s2 = "dbbca", When s3 = "aadbbcbcac", return t…

Problem link: http://oj.leetcode.com/problems/reverse-words-in-a-string/ Given an input string, reverse the string word by word. For example, Given s = "the sky is blue", return "blue is sky the". LeetCode OJ supports Python now! The s…

Given an array of integers, every element appears three times except for one. Find that single one. Note:Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory? 自己不会做... 搜答案,发现思路真是太巧妙了 关键:统计每一位上出现1的次…

Given an array of integers, every element appears three times except for one. Find that single one. Note:Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory? 题解:线性时间,O(1)的空间复杂度,只能把整数写成二进制的形式运算了.具体…

int singleNumber(int A[], int n) { int once = 0; int twice = 0; int three = 0; for (int i = 0; i < n; ++i) { //在计算新的once 前,计算twice twice |= once & A[i]; //计算新的once once ^= A[i]; three = ~(once & twice); //将3次的1都清理掉 once &= three; twice &…

今天做了三道LeetCode上的简单题目,每道题都是用c++和Python两种语言写的.由于c++版的代码网上比較多.所以就仅仅分享一下Python的代码吧,刚学完Python的基本的语法,做做LeetCode的题目还是不错的,对以后找工作面试也有帮助! 刚開始就从AC率最高的入手吧! 1.Given an array of integers, every element appears twice except for one. Find that single one. Note: Your…

Problem Link: https://oj.leetcode.com/problems/binary-tree-level-order-traversal-ii/ Use BFS from the tree root to traverse the tree level by level. The python code is as follows. # Definition for a binary tree node # class TreeNode: # def __init__(s…

Problem Link: http://oj.leetcode.com/problems/populating-next-right-pointers-in-each-node-ii/ OK... Exactly same to Populating Next Right Pointers in Each Node.…

Problem Link: http://oj.leetcode.com/problems/pascals-triangle-ii/ Let T[i][j] be the j-th element of the i-th row in the triangle, for 0 <= j <= i, i = 0, 1, ... And we have the recursive function for T[i][j] T[i][j] = 1, if j == 0 or j == i T[i][j…

Problem Link: http://oj.leetcode.com/problems/best-time-to-buy-and-sell-stock-ii/ We solve this problem using Greedy Algorithm, which only scan the prices list once. The worst-case running time is O(n). According to the problem description, we know t…

Problem link: http://oj.leetcode.com/problems/linked-list-cycle-ii/ The solution has two step: Detecting the loop using faster/slower pointers. Finding the begining of the loop. After two pointers meet in step 1, keep one pointer and set anther to th…

Problem Link: https://oj.leetcode.com/problems/maximum-depth-of-binary-tree/ Simply BFS from root and count the number of levels. The code is as follows. # Definition for a binary tree node # class TreeNode: # def __init__(self, x): # self.val = x #…

Problem Link: http://oj.leetcode.com/problems/triangle/ Let R[][] be a 2D array where R[i][j] (j <= i) is the minimum sum of the path from triangle[0][0] to tirangle[i][j]. We initialize R[0][0] = triangle[0][0], and update R[][] from i = 1 to n-1: R…

Problem Link: http://oj.leetcode.com/problems/best-time-to-buy-and-sell-stock-iii/ Linear Time Solution We try to solve this problem in O(n) time in the help of the algorithm in Best Time to Buy and Sell Stock, which can return the max profit by give…

Problem Link: http://oj.leetcode.com/problems/word-ladder/ Two typical techniques are inspected in this problem: Hash Table. One hash set is the words dictionary where we can check if a word is in the dictionary in O(1) time. The other hash set is us…

Problem Link: http://oj.leetcode.com/problems/longest-consecutive-sequence/ This problem is a classical problem where we can reduce the running time by the help of hash table. By given a list of numbers, we can find the longest consecutive sequence b…

# Definition for a binary tree node # class TreeNode: # def __init__(self, x): # self.val = x # self.left = None # self.right = None class Solution: # @param root, a tree node # @return an integer def sumNumbers(self, root): """ BFS the tre…