7. Reverse Integer

class Solution {
    public int reverse(int x) {
        int res = 0;
        while(x != 0) {
            int digit = x % 10;
            int temp = res * 10 + digit;
 
            if(temp / 10 != res){ //这里怕越界所以要verify一下，如果是特大数就返回0
                return 0;
            }
 
            res = temp;
            x /= 10;
        }
 
        return res;
    }
}

Given a signed 32-bit integer x, return x with its digits reversed. If reversing x causes the value to go outside the signed 32-bit integer range [-231, 231 - 1], then return 0.

Assume the environment does not allow you to store 64-bit integers (signed or unsigned).

Example 1:

Input: x = 123
Output: 321

Example 2:

Input: x = -123
Output: -321

Example 3:

Input: x = 120
Output: 21