- daily a LeetCode 】 【 9. Palindrome

Table of Contents

Original title:

Solution ideas:

codeImplementation:

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Original title:

Number of Palindromes

Gives you an integer x , returns true if x is a palindrome; otherwise, returns false .

Palindromic numbers are integers that read the same in positive order (from left to right) and in reverse order (from right to left).

For example, 121 is a palindrome, but 123 is not.

Example 1:

Input: x = 121Output: true

Example 2:

Input: x = -121output: falseExplanation: Read from left to right, as -121 .Reading from right to left, it is 121- .Therefore it is not a palindrome.

Example 3:

Input: x = 10output: falseExplanation: Read from right to left as 01 .Therefore it is not a palindrome.

Solution ideas:

First understand the concept of palindrome correctly.We know that negative numbers and numbers with 0 at the end cannot be palindromic numbers, so these two are used as boundaries and are false.The other numbers are palindrome numbers.First of all, you can solve the problem like this: determine whether the first and last digit of the number are consistent. If they are different, it is not a palindrome, and two are compared each time, that is, a left and a right must be set, and the left andWhether the right is consistent or not, it returns false.

Compare the corresponding numbers in the integers by rounding and remainder operations.

For example:

1221 is the number.By calculating 1221 / 1000, get the first 1
By calculating 1221 % 10, you can get the last 1
Compare
Then take 22 out to continue the comparison

Code implementation:

class Solution {public boolean isPalindrome(int x) {//Boundary judgmentif(x<0||(x%10==0&&x!=0)){return false;}int ret=1;while(x/ret>=10){ret*=10;}while(x>0){int left=x/ret;int right=x%10;if(left!=right){return false;}x=(x%ret)/10;ret/=100;}return true;}}

Run result: