Ruizhi Ma's Blog

Problem 36

Valid Sudoku

问题描述 https://leetcode.com/problems/valid-sudoku/ 解决思路遍历对每一行判断；遍历对每一列判断；遍历对每3*3的小方块内部遍历问题解惑 row < (i / 3) * 3 + 3是什么意思？更具i从0~9，(i / 3) * 3 + 3的结果依次是：3-3-3-6-6-6-9-9-9。这将i=0~3的时候，row限制在前三个...

Posted by Ruizhi Ma on July 21, 2019

Problem 35

Search Insert Position

问题描述 https://leetcode.com/problems/search-insert-position/ 解决思路一比较简单，直接遍历数组，不断地将小于target的元素的下标加1给target就可以。代码一 class Solution { public int searchInsert(int[] nums, int target) { //c...

Posted by Ruizhi Ma on July 20, 2019

Problem 34

Find First and Last Position of Element in Sorted Array

问题描述 https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array/ 解决思路遇到排序数组中找元素，首推二分法。分别找首尾两个元素，获得下标后返回。问题解惑我当时以为findFirst和findLast两个函数一模一样，不就是if else调换了一下嘛？实则不然，关键在...

Posted by Ruizhi Ma on July 20, 2019

Problem 33

Search in Rotated Sorted Array

问题描述 https://leetcode.com/problems/search-in-rotated-sorted-array/ 解决思路遇到这种排序的，还是首推二分法。这个题里面不管从哪里旋转，一定有一段是升序排列的。分情况讨论：1. 如果mid刚好在有序的里面怎么办？ 2. 如果mid在有序的外面怎么办？具体看代码，走一遍就看懂了代码 class Solution { ...

Posted by Ruizhi Ma on July 19, 2019

Problem 31

Next Permutation

问题描述 https://leetcode.com/problems/next-permutation/ 解决思路不太会，没能理解。只能先把代码贴上来。问题解惑代码 class Solution { public void nextPermutation(int[] nums) { if(nums == null || nums.length == 0) ...

Posted by Ruizhi Ma on July 18, 2019

Problem 196

Delete Duplicate Emails

问题描述 https://leetcode.com/problems/delete-duplicate-emails/ 代码 # Write your MySQL query statement below DELETE p1 FROM Person as p1, Person as p2 WHERE p1.Email = p2.Email AND p1.Id > p2.Id;

Posted by Ruizhi Ma on July 17, 2019

Problem 182

Duplicate Email

问题描述题目看链接：https://leetcode.com/problems/duplicate-emails/ 解决思路 Inner join相当于取两个表的交集；Distinct是返回唯一不同的值。代码 # Write your MySQL query statement below SELECT DISTINCT tb1.Email FROM Person as tb1 IN...

Posted by Ruizhi Ma on July 17, 2019

Problem 29

Divide Two Integers

问题描述 https://leetcode.com/problems/divide-two-integers/ 解决思路这道题不可以用除法，不可以用取模运算。举例35和3，思路如下： 3«0,3 3«1,6 3«2,12 3«3,24 3«4,48. 此时48>35,所以只能左移3次到24,38等于24，留下8.此时35-24=11 3«0,3 3«1,6 3«2,12 此...

Posted by Ruizhi Ma on July 16, 2019

Problem 9

Palindrome Number

问题描述 Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward. Example 1: Input: 121 Output: true Example 2: Input: -121 Output: false ...

Posted by Ruizhi Ma on July 12, 2019

Problem 8

问题描述 https://leetcode.com/problems/string-to-integer-atoi/ 解决思路直接看代码吧，题目就是有点麻烦，不是很难，注释把思路写的够清晰了代码 class Solution { public int myAtoi(String str) { //process the whitespace ...