Ivan 的专栏

Leetcode 第 794 题(Valid Tic-Tac-Toe State） A Tic-Tac-Toe board is given as a string array board. Return True if and only if it is possible to reach this board position during the course of a valid ...

LeetCode 第 73 题 (Set Matrix Zeroes) Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place. Follow up: Did you use extra space? A straight forward sol

LeetCode 第 367 题 (Valid Perfect Square) 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 su

LeetCode 第 72 题 (Super Pow) Your task is to calculate ab mod 1337 where a is a positive integer and b is an extremely large positive integer given in the form of an array. Example1: a = 2

LeetCode 第 19 题 (Remove Nth Node From End of List) Given a linked list, remove the nth node from the end of list and return its head. For example, Given linked list: 1->2->3->4->5, and n = 2.

LeetCode 第 292 题 （Nim Game） 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 remov

LeetCode 第 67 题 (Add Binary) Given two binary strings, return their sum (also a binary string). For example, a = “11” b = “1” Return “100”.两个字符串，计算加法。这道题主要是考察对字符串操作的掌握情况。另外，加法要从低位算起，但是

LeetCode 第 204 题 (Count Primes) Description: Count the number of prime numbers less than a non-negative number, n.计算小于 N 的素数的个数。这道题目比较简单。但是想提高计算效率与需要费点脑筋。判断一个数字 nn 是不是素数的简单方法是 用 nn 去除 2,3,4,…,n−1

LeetCode 第 371 题 （Sum of Two Integers） Calculate 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, return 3.不用加减法计算两个整数的和。这道

LeetCode 第 263 题 （Ugly Number） Write a program to check whether a given number is an ugly number. Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 6, 8 ar

LeetCode 第 155 题 (Min Stack) 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 o

LeetCode 第 344 题(Reverse String) Write a function that takes a string as input and returns the string reversed. Example: Given s = “hello”, return “olleh”. 这道题非常简单。用 C++ 来写的话主要是考察对 string 类型

LeetCode 第 345 题(Reverse Vowels of a String) Write a function that takes a string as input and reverse only the vowels of a string. Example 1: Given s = “hello”, return “holle”. Example 2:

LeetCode 第 14 题(Longest Common Prefix) Write a function to find the longest common prefix string amongst an array of strings. 这道题比较简单，主要是要考虑一些特殊情况，比如这个 vector 为空如何处理。下面是我的代码。class Solution {public:

LeetCode 第 21 题 (Merge Two Sorted Lists) Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.合并两个排好序的链表，要求合并之

LeetCode 第 66 题 (Plus One) Given a non-negative number represented as an array of digits, plus one to the number. The digits are stored such that the most significant digit is at the head of the l

LeetCode 第 65 题(Valid Number) Validate if a given string is numeric. Some examples: “0” => true ” 0.1 ” => true “abc” => false “1 a” => false “2e10” => true Note: It is inten

LeetCode 第 69 题 (Sqrt(x)) Implement int sqrt(int x). Compute and return the square root of x.求 x 的平方根。我们知道 x√\sqrt{x} 是单调增函数， 1≤x√≤x1 \leq \sqrt{x} \leq x。所以可以用二分查找法来计算。int mySqrt(int x){ if

LeetCode 第 50 题 (Pow(x, n)) Implement pow(x, n).这个题目非常简短，求 xnx^n。其中nn 为整数。 最简单的想法就是用一个循环，将 xx 自乘nn 次。按照这个思路有下面的代码。class Solution {public: double myPow(double x, int n) { int sign

LeetCode 第 343 题 (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 ge

LeetCode 第 125 题 (Valid Palindrome) Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases. For example, “A man, a plan, a canal: Panama”

LeetCode 第 326 题 （Power of Three） Given an integer, write a function to determine if it is a power of three. Follow up: Could you do it without using any loop / recursion?这道题的常规的思路是不停的除以 3，如果能

LeetCode 第 338 题 (Counting Bits) Given 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 representation and return them as an

LeetCode 第 37 题 (Sudoku Solver) Write a program to solve a Sudoku puzzle by filling the empty cells. Empty cells are indicated by the character ‘.’. You may assume that there will be only on...

LeetCode 第 190 题 (Reverse Bits) Reverse bits of a given 32 bits unsigned integer. For example, given input 43261596 (represented in binary as 00000010100101000001111010011100), return 964176192

LeetCode 第 191 题 (Number of 1 Bits) 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

LeetCode 第 231 题 (Power of Two) Given an integer, write a function to determine if it is a power of two.这个题目有个特别简单的解法。当然，能够独自想出这个方法可不简单。这种方法可以作为一个知识点记住就好了。class Solution {public: bool isPowerOf

LeetCode 第 342 题 Given an integer (signed 32 bits), write a function to check whether it is a power of 4. Example: Given num = 16, return true. Given num = 5, return false. Follow up: Co

LeetCode 第 9 题 Determine whether an integer is a palindrome. Do this without extra space. Some hints: Could negative integers be palindromes? (ie, -1) If you are thinking of converting t

LeetCode 第 7 题题目是这样的: Reverse digits of an integer. Example1: x = 123, return 321 Example2: x = -123, return -321 Here are some good questions to ask before coding. Bonus points for you

LeetCode 第三题 Given a string, find the length of the longest substring without repeating characters. Examples: Given “abcabcbb”, the answer is “abc”, which the length is 3. Given “bbbbb”,

Leetcode 第二题详解题目如下： Question You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the

Leetcode 第一题昨天去逛了逛这个网站，感觉挺有意思。准备有空的时候就做一两道。第一道题目是这样的： Given an array of integers, return indices of the two numbers such that they add up to a specific target. You may assume that each input wou