LouisLan的学习简记 👋🏼

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 ....

题目地址 https://leetcode.com/problems/permutation-sequence/ 题目描述 The set [1,2,3,..., _n_ ] contains a total of n! unique permutations. By listing and labeling all of the permutations in order, we get the following sequence for n = 3: "123" "132" "213" "231" "312" "321" Given n and k , return the k th permutation sequence. Note: Given n will be between 1 and 9 inclusive. Given k will be between 1 and n! inclusive. Example 1: Input: n = 3, k = 3 Output: "213" Example 2: Input: n = 4, k = 9 Outpu....

题目地址 https://leetcode.com/problems/spiral-matrix-ii/ 题目描述 Given a positive integer n , generate a square matrix filled with elements from 1 to n 2 in spiral order. Example: Input: 3 Output: [ [ 1, 2, 3 ], [ 8, 9, 4 ], [ 7, 6, 5 ] ] 思路 此题跟之前那道 Spiral Matrix 本质上没什么区别，就相当于个类似逆运算的过程，这道题是要按螺旋的顺序来填数，由于给定矩形是个正方形，我们计算环数时用 n / 2 来计算，若 n 为奇数时，此时最中间的那个点没有被算在环数里，所以最后需要单独赋值，还是下标转换问题是难点，参考之前 Spiral Matrix 的讲解来转换下标吧。 关键点解析 代码 解法一： class Solution { public: vector<vector<int>> generateMatrix(int n) ....

题目地址 https://leetcode.com/problems/length-of-last-word/ 题目描述 Given a string s consists of upper/lower-case alphabets and empty space characters ' ', return the length of last word in the string. If the last word does not exist, return 0. Note: A word is defined as a character sequence consists of non-space characters only. Example: Input: "Hello World" Output: 5 思路 这道题难度不是很大。先对输入字符串做预处理，去掉开头和结尾的空格，然后用一个计数器来累计非空格的字符串的长度，遇到空格则将计数器清零。 关键点解析 代码 解法一： class Solution { public: int lengthOfLastWord(str....

题目地址 https://leetcode.com/problems/insert-interval/ 题目描述 Given a set of non-overlapping intervals, insert a new interval into the intervals (merge if necessary). You may assume that the intervals were initially sorted according to their start times. Example 1: Input: intervals = [[1,3],[6,9]], newInterval = [2,5] Output: [[1,5],[6,9]] Example 2: Input: intervals = [[1,2],[3,5],[6,7],[8,10],[12,16]], newInterval = [4,8] Output: [[1,2],[3,10],[12,16]] Explanation: Because the new interval [4,8] o....

题目地址 https://leetcode.com/problems/merge-intervals/ 题目描述 Given a collection of intervals, merge all overlapping intervals. Example 1: Input: [[1,3],[2,6],[8,10],[15,18]] Output: [[1,6],[8,10],[15,18]] Explanation: Since intervals [1,3] and [2,6] overlaps, merge them into [1,6]. Example 2: Input: [[1,4],[4,5]] Output: [[1,5]] Explanation: Intervals [1,4] and [4,5] are considered overlapping. NOTE: input types have been changed on April 15, 2019. Please reset to default code definition to get ne....