[leetcode]9. Palindrome Number 回文数

Posted 2021-11-25 liuliu5151

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
Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.

Example 3:

Input: 10
Output: false
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?

 

题意：

判断是否为回文数

 

Solution1:  reverse the original number as reversedInt,  if reversedInt == original number,  it is a Palindrome 

      original number     reversedInt      isPalindrome()

        123                       321                flase

        121                        121                true

 

code:

 1  /*
 2 Time Complexity:  O(n), loop each digit of input number 
 3 Space Complexity: O(1), allocate a variable temp
 4 */
 5 
 6 class Solution {
 7     public boolean isPalindrome(int x) {
 8         // handle input is negative  like -121 or end with 0 
 9         if (x < 0 || (x != 0 && x % 10 == 0)) return false;
10 
11         int temp = x;
12         int reverseInt = 0;
13         while (x != 0) {
14             reverseInt = reverseInt * 10 + x % 10;
15             x = x / 10;
16         }
17         return (reverseInt == temp);
18     }
19 }