2. Add Two Numbers https://leetcode.com/problems/add-two-numbers/description/ class Solution { public: ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) { ListNode result(-); ListNode* current = &result; ; while(l1!=NULL || l2!=NULL){ ; ; if(l1!=NU…

题目: Given a non-negative integer num, repeatedly add all its digits until the result has only one digit. For example: Given num = 38, the process is like: 3 + 8 = 11, 1 + 1 = 2. Since 2 has only one digit, return it. Follow up: Could you do it withou…

https://leetcode.com/problems/integer-break/ 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. For example, given n = 2, return 1 (2…

math(leetcode) 小结 在leetcode中有些知识点(套路) 判断一个数是不是能被某些数整除,可以用 n%x == 0,循环除的话,就将while(n%x == 0)的循环条件设置判断整除(取余),然后除该数后在继续判断. 231.power of two(判断一个数是不是2的幂) class Solution { public: bool isPowerOfTwo(int n) { ) return false; ) return true; == ) { n = n / ; }…

https://leetcode.com/problems/integer-to-english-words/ Convert a non-negative integer to its english words representation. Given input is guaranteed to be less than 231 - 1. For example, 123 -> "One Hundred Twenty Three" 12345 -> "Tw…

For a web developer, it is very important to know how to design a web page's size. So, given a specific rectangular web page’s area, your job by now is to design a rectangular web page, whose length L and width W satisfy the following requirements: 1…

You have a total of n coins that you want to form in a staircase shape, where every k-th row must have exactly k coins. Given n, find the total number of full staircase rows that can be formed. n is a non-negative integer and fits within the range of…

Given a non-negative integer num, repeatedly add all its digits until the result has only one digit. Example: Input: 38 Output: 2 Explanation: The process is like: 3 + 8 = 11, 1 + 1 = 2.   Since 2 has only one digit, return it. Follow up:Could you do…

一.204. Count Primes Count the number of prime numbers less than a non-negative number, n. Input: 10 Output: 4 Explanation: There are 4 prime numbers less than 10, they are 2, 3, 5, 7. 1.数学原理:两个质数的乘积一定是合数.一个质数乘以任何数的积都一定不是质数.(除了1) 2.代码:需要注意的点:for (int…

Given an integer, return its base 7 string representation. Example 1: Input: 100 Output: "202" Example 2: Input: -7 Output: "-10" Note: The input will be in range of [-1e7, 1e7]. 不停除以7, 然后把余数放到ans里面, 最后reverse ans加上符号即可. Code class Sol…

做个基本思路可以用 brute force, 但时间复杂度较高. 因为起始值都为0, 所以肯定是左上角的重合的最小的长方形就是结果, 所以我们求x, y 的最小值, 最后返回x*y. Code     T: O(m*n)    S: O(1) class Solution: def rangeAddition2(self, m, n, ops): for op1, op2 in ops: m = min(m, op1) n = min(n, op2) return m*n…

Given a positive integer num, write a function which returns True if num is a perfect square else False. Note: Do not use any built-in library function such as sqrt. Example 1: Input: 16 Returns: True Example 2: Input: 14 Returns: False Use Newton Me…

You 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 to 3 stones. The one who removes the last stone will be the winner. You will take the first turn to remove th…

Given a positive integer, return its corresponding column title as appear in an Excel sheet. For example: 1 -> A 2 -> B 3 -> C ... 26 -> Z 27 -> AA 28 -> AB ... Example 1: Input: 1 Output: "A" Example 2: Input: 28 Output: "…

Given an integer n, return the number of trailing zeroes in n!. Example 1: Input: 3 Output: 0 Explanation: 3! = 6, no trailing zero. Example 2: Input: 5 Output: 1 Explanation: 5! = 120, one trailing zero. Note: Your solution should be in logarithmic…

A self-dividing number is a number that is divisible by every digit it contains. For example, 128 is a self-dividing number because 128 % 1 == 0, 128 % 2 == 0, and 128 % 8 == 0. Also, a self-dividing number is not allowed to contain the digit zero. G…

There are 1000 buckets, one and only one of them contains poison, the rest are filled with water. They all look the same. If a pig drinks that poison it will die within 15 minutes. What is the minimum amount of pigs you need to figure out which bucke…

[263] Ugly Number [Easy] 一个数的质因子只有2,3,5就叫丑数,写个函数判断丑数. //Author: Wanying //注意 0 和 1 的corner case, 你居然还没一次AC== //想好了再写,不然等着挂吧==!!!!! class Solution { public: bool isUgly(int num) { || num == ) { return num; } == ) { num = num / ; } == ) { num = num / ;…

题目链接:Balanced Binary Tree | LeetCode OJ Given a binary tree, determine if it is height-balanced. For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more tha…

Suppose we abstract our file system by a string in the following manner: The string "dir\n\tsubdir1\n\tsubdir2\n\t\tfile.ext" represents: dir subdir1 subdir2 file.ext The directory dir contains an empty sub-directory subdir1 and a sub-directory …

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 product = 6. 这个求最大子数组乘积问题是由最大子数组之和问题演变而来,但是却比求最大子数组之和要复…

Given n points on a 2D plane, find the maximum number of points that lie on the same straight line. 这道题给了我们一堆二维点,然后让我们求最大的共线点的个数,根据初中数学我们知道,两点确定一条直线,而且可以写成y = ax + b的形式,所有共线的点都满足这个公式.所以这些给定点两两之间都可以算一个斜率,每个斜率代表一条直线,对每一条直线,带入所有的点看是否共线并计算个数,这是整体的思路.但是还有…

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, 3, 4]. Return its length: 4. Your algorithm should run i…

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 (ie, buy one and sell one share of the stock), design an algorithm to find the maximum profit. 这道题相…

Given a binary tree, find its maximum depth. The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node. 求二叉树的最大深度问题用到深度优先搜索DFS,递归的完美应用,跟求二叉树的最小深度问题原理相同.代码如下: C++ 解法一: class Solution { public: in…

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? 这个爬梯子问题最开始看的时候没搞懂是让干啥的,后来看了别人的分析后,才知道实际上跟斐波那契数列非常相似,假设梯子有n层,那么如何爬到第n层呢,因为每次只能怕1或2步,那…

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,−1,2,1] has the largest sum = 6. click to show more practice. Mor…

Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it is able to trap after raining. For example, Given [0,1,0,2,1,0,1,3,2,1,2,1], return 6. The above elevation map is represented by a…

Write a function to find the longest common prefix string amongst an array of strings. 这道题让我们求一系列字符串的共同前缀,没有什么特别的技巧,无脑查找即可,我们定义两个变量i和j,其中i是遍历搜索字符串中的字符,j是遍历字符串集中的每个字符串.这里将单词上下排好,则相当于一个各行长度有可能不相等的二维数组,我们遍历顺序和一般的横向逐行遍历不同,而是采用纵向逐列遍历,在遍历的过程中,如果某一行没有了,说明其为…

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 two lines, which together with x-axis forms a containe…