Palindrome Number（判断一个整数是否是回文串） leetcode9

古城微笑少年丶 2022-05-24 00:23 227阅读 0赞

Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.

Example 1:

  1. Input: 121
  2. Output: true

Example 2:

  1. Input: -121
  2. Output: false
  3. Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.

Example 3:

  1. Input: 10
  2. Output: false
  3. Explanation: Reads 01 from right to left. Therefore it is not a palindrome.

Follow up:

Coud you solve it without converting the integer to a string?

  1. public boolean isPalindrome(int x) {
  2.         if(x<0)
  3.             return false;
  4.         String res=x+"";
  5.         //String res=Integer.toString(x);
  6.         //排除‘-’的回文串
  7.         //if(res.charAt(0)=='-')
  8.             //res=res.substring(1);
  10.         int middle=res.length()/2;
  11.         if(res.length()%2==0){
  12.             for(int i=middle-1,j=middle;i>=0&&j<res.length();){
  13.                 if(res.charAt(i--)!=res.charAt(j++))
  14.                     return false;
  15.             }
  16.         }else{
  17.             for(int i=middle-1,j=middle+1;i>=0&&j<res.length();){
  18.                 if(res.charAt(i--)!=res.charAt(j++))
  19.                     return false;
  20.             }
  21.         }
  22.         return true;
  24.     }

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