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Given an integer n, return the number of trailing zeroes in n!. Note: Your solution should be in logarithmic time complexity. 解题思路：只有因子2和因子5相乘会产生10，同时因为因子2的数量大于因子5的数量，所以只需看序列中因子5的个数。它可以通过n/5得到，同

Related to question Excel Sheet Column Title Given a column title as appear in an Excel sheet, return its corresponding column number. For example: A -> 1 B -> 2 C -> 3 ...

A peak element is an element that is greater than its neighbors.Given an input array where num[i] ≠ num[i 1], find a peak element and return its index.The array may contain multiple peaks, in that case

Suppose a sorted array 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).Find the minimum element.You may assume no duplicate exists in the array.

Find the contiguous subarray within an array (containing at least one number) which has the largest product.For example, given the array [2,3,-2,4], the contiguous subarray [2,3] has the largest produ

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

Follow up for “Find Minimum in Rotated Sorted Array”:What if duplicates are allowed?Would this affect the run-time complexity? How and why?Suppose a sorted array is rotated at some pivot unknown to you

Write a program to find the node at which the intersection of two singly linked lists begins.For example, the following two linked lists:begin to intersect at node c1. 解题思路 首先把两个链表的所有非空结点入栈，然后比较栈顶元素并出

Compare two version numbers version1 and version2. If version1 > version2 return 1, if version1 version2 return -1, otherwise return 0. You may assume that the version strings are non-empty and co

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.push(x) – Push element x onto stack. pop() – Removes the element on top of the stack. top() – Get the

Say you have an array for which the ithi^{th} element is the price of a given stock on day ii.Design an algorithm to find the maximum profit. You may complete as many transactions as you like (ie, buy

Given an input string, reverse the string word by word.For example, Given s = “the sky is blue”, return “blue is sky the”.Clarification:1.What constitutes a word? A sequence of non-space characters

Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and set.get(key) - Get the value (will always be positive) of the key if the k

Say you have an array for which the ithi^{th} element is the price of a given stock on day ii.Design an algorithm to find the maximum profit. You may complete at most two transactions.Note: You may no

Evaluate the value of an arithmetic expression in Reverse Polish Notation.Valid operators are , -, *, /. Each operand may be an integer or another expression.Some examples: ["2", "1", " ", "3", "*"]

Given n points on a 2D plane, find the maximum number of points that lie on the same straight line. 解题思路 若两个点共线，则有如下情况：两个点重合 两个点的x坐标相同（斜率无穷大） 两个点的斜率相同

Given an unsorted array, find the maximum difference between the successive elements in its sorted form.Try to solve it in linear time/space.Return 0 if the array contains less than 2 elements.You may

Say you have an array for which the ithi^{th} element is the price of a given stock on day ii.If you were only permitted to complete at most one transaction (ie, buy one and sell one share of the stock

Given a binary tree, return the preorder traversal of its nodes’ values.For example: Given binary tree {1,#,2,3}, return [3,2,1].Note: Recursive solution is trivial, could you do it iteratively?递归

Rotate an array of n elements to the right by k steps.For example, with n=7n = 7 and k=3k = 3, the array [1,2,3,4,5,6,7][1,2,3,4,5,6,7] is rotated to [5,6,7,1,2,3,4][5,6,7,1,2,3,4].Note: Try to come u

Given a binary tree, return the postorder traversal of its nodes’ values.For example: Given binary tree {1,#,2,3}, return [3,2,1].Note: Recursive solution is trivial, could you do it iteratively?

All DNA is composed of a series of nucleotides abbreviated as A, C, G, and T, for example: “ACGAATTCCG”. When studying DNA, it is sometimes useful to identify repeated sequences within the DNA.Write a

Sort a linked list in O(n log n) time using constant space complexity. 可以利用归并排序解决该问题。普通的归并排序算法时间复杂度为O(nlogn)，空间复杂度为O(n)，因为需要建立两个数组来存储原来数组的值，这两个数组的长度加起来恰好为原数组的长度。但是对于链表可以省去复制两个已经排好序的数组的操作，从而使空间复杂度

Sort a linked list using insertion sort. 解题思路 对于得到结点current的插入位置，从头结点开始遍历，直到遍历到值大于等于节点current的结点，然后将从该结点到current的前驱结点的所有结点的值依次和current结点的值交换，从而达到将该节点插入所遍历到的位置的目的。

Reverse bits of a given 32 bits unsigned integer.For example, given input 43261596 (represented in binary as 00000010100101000001111010011100), return 964176192 (represented in binary as 00111001011110

Write a function that takes an unsigned integer and returns the number of ’1’ bits it has (also known as the Hamming weight).For example, the 32-bit integer ’11’ has binary representation 0000000000000

One measure of `unsortedness` in a sequence is the number of pairs of entries that are out of order with respect to each other. For instance, in the letter sequence `DAABEC`, this measure is 5, since D is great

Given a singly linked list L: L0→L1→…→Ln−1→LnL_0→L_1→…→L_{n-1}→L_n, reorder it to: L0→Ln→L1→Ln−1→L2→Ln−2→…L_0→L_n→L_1→L_{n-1}→L_2→L_{n-2}→…You must do this in-place without altering the nodes’ values.

Given a linked list, return the node where the cycle begins. If there is no cycle, return null.Follow up: Can you solve it without using extra space?解题思路设链表长度为n，头结点与循环节点之间的长度为k。定义两个指针slow和fast，slow每次走

Given a linked list, determine if it has a cycle in it.Follow up: Can you solve it without using extra space?解题思路使用快慢两个指针，如果快的指针赶上了慢的，则说明存在回路。实现代码/** * Definition for singly-linked list. * struct Li

Given two strings s and t, determine if they are isomorphic.Two strings are isomorphic if the characters in s can be replaced to get t.All occurrences of a character must be replaced with another chara

Given a range [m, n] where 0 <= m <= n <= 2147483647, return the bitwise AND of all numbers in this range, inclusive.For example, given the range [5, 7], you should return 4.解题思路① n&(n-1)，可以去除n的最低位的1。

You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed, the only constraint stopping you from robbing each of them is that adjacent houses

Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.For example: Given the following binary tree, 1

Description: Count the number of prime numbers less than a non-negative number, n解题思路采用Eratosthenes筛选法，依次分别去掉2的倍数，3的倍数，5的倍数，……，最后剩下的即为素数。实现代码class Solution { public: int countPrimes(int n) {

Remove all elements from a linked list of integers that have value val. Example Given: 1 –> 2 –> 6 –> 3 –> 4 –> 5 –> 6, val = 6 Return: 1 –> 2 –> 3 –> 4 –> 5解题思路定义两个指针pre和cur，如果cur的值为val，则删除该结点。需要注意

Given a 2d grid map of '1's (land) and '0's (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume

Reverse a linked list from position m to n. Do it in-place and in one-pass.For example: Given 1->2->3->4->5->NULL, m = 2 and n = 4,return 1->4->3->2->5->NULL.Note: Given m, n satisfy the following co

Reverse a singly linked list.解题思路对于非递归实现，思路是依次将从第二个结点到最后一个结点的后继设为头结点，然后将该节点设为头结点（需记住将原头结点的后继设为空）。 对于递归实现，首先反转从第二个结点到最后一个结点的链表，然后再将头结点放到已反转链表的最后，函数返回新链表的头结点。递归实现代码1//Runtime:10 ms class Solution { publ

Problem Description Hey, welcome to HDOJ(Hangzhou Dianzi University Online Judge). In this problem, your task is to calculate SUM(n) = 1 + 2 + 3 + … + n. Input The input will consist of a series o