palindrome-number

题目描述

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.

 解一：

 按数字计算

public class Solution {
    public boolean isPalindrome(int x) {
        int temp = 1 ,y = x;
        if(x<0)
            return false;
        if(x<10 && x>=0)
            return true;
        while(y != 0){
            temp = temp *10; 
            y = y /10;
            if(y<10)
                break;
        }
        while(temp >= 10 && x >= 10){
            int r = x % 10;
            int l = x / temp;
            if(r != l)
                return false;
            x = (x % temp) /10;
            temp = temp /100;
        }
        return true;
    }
}

　　

解二：

 字符串计算：

public class Solution {
    public static boolean isPalindrome(int x) {
        String arrays = "";
        int temp, flag = 0;
        if (x == 0)
            return true;
        if (x < 0  || x % 10 == 0)
            return false;
        while (x > 0) {
            temp = x - (x / 10) * 10;
            arrays = arrays + temp;
            x = x / 10;
        }
        for (int i = 0; i < arrays.length(); i++) {
            if (arrays.charAt(i) == arrays.charAt(arrays.length() - i - 1)) {
                flag = 1;
            } else {
                flag = 0;
                break;
            }
        }
        if (flag == 1)
            return true;
        else
            return false;
    }
}