LouisLan的学习简记 👋🏼

题目地址 https://leetcode.com/problems/climbing-stairs/ 题目描述 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? Note: Given n will be a positive integer. Example 1: Input: 2 Output: 2 Explanation: There are two ways to climb to the top. 1. 1 step + 1 step 2. 2 steps Example 2: Input: 3 Output: 3 Explanation: There are three ways to climb to the top. 1. 1 step + 1 step + 1 step 2. 1 ste....

题目地址 https://leetcode.com/problems/sqrtx/ 题目描述 Implement int sqrt(int x). Compute and return the square root of x, where x is guaranteed to be a non-negative integer. Since the return type is an integer, the decimal digits are truncated and only the integer part of the result is returned. Example 1: Input: 4 Output: 2 Example 2: Input: 8 Output: 2 Explanation: The square root of 8 is 2.82842..., and since the decimal part is truncated, 2 is returned. 思路 这道题要求我们求平方根，我们能想到的方法就是算一个候选值的平方，然后和 x 比较大小....

题目地址 https://leetcode.com/problems/text-justification/ 题目描述 Given an array of words and a width maxWidth , format the text such that each line has exactly maxWidth characters and is fully (left and right) justified. You should pack your words in a greedy approach; that is, pack as many words as you can in each line. Pad extra spaces ' ' when necessary so that each line has exactly maxWidth characters. Extra spaces between words should be distributed as evenly as possible. If the number of spaces....

题目地址 https://leetcode.com/problems/add-binary/ 题目描述 Given two binary strings, return their sum (also a binary string). The input strings are both non-empty and contains only characters 1 or 0. Example 1: Input: a = "11", b = "1" Output: "100" Example 2: Input: a = "1010", b = "1011" Output: "10101" 思路 二进制数相加，并且保存在 string 中，要注意的是如何将 string 和 int 之间互相转换，并且每位相加时，会有进位的可能，会影响之后相加的结果。而且两个输入 string 的长度也可能会不同。这时我们需要新建一个 string，它的长度是两条输入 string 中的较大的那个，并且把较短的那个输入 string 通过在开头加字符‘0’来补的较大的那个长度。这时候我们逐个从两个 s....

题目地址 https://leetcode.com/problems/plus-one/ 题目描述 Given a non-empty array of digits representing a non-negative integer, plus one to the integer. The digits are stored such that the most significant digit is at the head of the list, and each element in the array contain a single digit. You may assume the integer does not contain any leading zero, except the number 0 itself. Example 1: Input: [1,2,3] Output: [1,2,4] Explanation: The array represents the integer 123. Example 2: Input: [4,3,2,1] Ou....

题目地址 https://leetcode.com/problems/valid-number/ 题目描述 Validate if a given string can be interpreted as a decimal number. Some examples: "0" => true " 0.1 " => true "abc" => false "1 a" => false "2e10" => true " -90e3 " => true " 1e" => false "e3" => false " 6e-1" => true " 99e2.5 " => false "53.5e93" => true " --6 " => false "-+3" => false "95a54e53" => false Note: It is intended for the problem statement to be ambiguous. You should gather all requiremen....

题目地址 https://leetcode.com/problems/minimum-path-sum/ 题目描述 Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right which minimizes the sum of all numbers along its path. Note: You can only move either down or right at any point in time. Example: Input: [ [1,3,1], [1,5,1], [4,2,1] ] Output: 7 Explanation: Because the path 1→3→1→1→1 minimizes the sum. 思路 这道题给了我们一个只有非负数的二维数组，让找一条从左上到右下的路径，使得路径和最小，限定了每次只能向下或者向右移动。一个常见的错误解法就是每次走右边或下边数字中较小的那个，这样的贪婪算法获得的局部最优解不一定是全....

题目地址 https://leetcode.com/problems/unique-paths-ii/ 题目描述 A robot is located at the top-left corner of a m x n grid (marked 'Start' in the diagram below). The robot can only move either down or right at any point in time. The robot is trying to reach the bottom-right corner of the grid (marked 'Finish' in the diagram below). Now consider if some obstacles are added to the grids. How many unique paths would there be? An obstacle and empty space is marked as 1 and 0 respectively in the grid. Note:....

题目地址 https://leetcode.com/problems/unique-paths/ 题目描述 A robot is located at the top-left corner of a m x n grid (marked 'Start' in the diagram below). The robot can only move either down or right at any point in time. The robot is trying to reach the bottom-right corner of the grid (marked 'Finish' in the diagram below). How many possible unique paths are there? Above is a 7 x 3 grid. How many possible unique paths are there? Note: m and n will be at most 100. Example 1: Input: m = 3, n = 2 Out....

题目地址 https://leetcode.com/problems/rotate-list/ 题目描述 Given a linked list, rotate the list to the right by k places, where k is non-negative. Example 1: Input: 1->2->3->4->5->NULL, k = 2 Output: 4->5->1->2->3->NULL Explanation: rotate 1 steps to the right: 5->1->2->3->4->NULL rotate 2 steps to the right: 4->5->1->2->3->NULL Example 2: Input: 0->1->2->NULL, k = 4 Output: 2->0->1->NULL Explanation: rotate 1 steps to the ....