7 Reverse Integer

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

Example 4:

Input: x = 0
Output: 0

Constraints:

-2^31 <= x <= 2^31 - 1

---

用 long 来计算，不会溢出，如果超出 int 的范围，返回 0

class Solution {
    public int reverse(int x) {
        long res=0;
        while(x!=0){
            res=res*10+x%10;;
            x/=10;
        }
        if(res>Integer.MAX_VALUE || res<Integer.MIN_VALUE) return 0;
        return (int)res;
    }
}