leetcode : Palindrome Number

Determine whether an integer is a palindrome. Do this without extra space.

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Some hints:

Could negative integers be palindromes? (ie, -1)

If you are thinking of converting the integer to string, note the restriction of using extra space.

You could also try reversing an integer. However, if you have solved the problem "Reverse Integer", you know that the reversed integer might overflow. How would you handle such case?

There is a more generic way of solving this problem.

 

思路: 除法 + 求模

 

public class Solution {
    public boolean isPalindrome(int x) {
       long tmp = 0;
       long original = x;
       if(x < 0) {
           return false;
       }
       if(x == 0) {
           return true;
       }
       while(x != 0) {
           tmp = tmp * 10 + x % 10;
           x = x / 10;
       }
       
       if(tmp == original) {
           return true;
       } else {
           return false;
       }
      
    }
}

  

一种更牛逼的解法, 不需要判断overflow

 

 

public boolean isPalindrome(int x) {
    if (x<0 || (x!=0 && x%10==0)) return false;
    int rev = 0;
    while (x>rev){
    	rev = rev*10 + x%10;
    	x = x/10;
    }
    return (x==rev || x==rev/10);
}

  

posted @ 2017-02-08 11:00  notesbuddy  阅读(106)  评论(0编辑  收藏  举报