7. Reverse Integer

Given a 32-bit signed integer, reverse digits of an integer.

Example 1:

Input: 123
Output:  321

 

Example 2:

Input: -123
Output: -321

 

Example 3:

Input: 120
Output: 21

 

Note:
Assume we are dealing with an environment which could only hold integers within the 32-bit signed integer range. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

思路：用一个long型来解决overflow问题。

class Solution {
public:
    int reverse(int x) {
        bool isActive=true;
        if(x<0)
        {
            x=-x;
            isActive=false;
        }
        long reverseX=0;
        while(x)
        {
            reverseX=reverseX*10+x%10;
            x=x/10;
        }
        if(!isActive)reverseX=-reverseX;
        if(reverseX>INT_MAX || reverseX<INT_MIN)return 0;
        return reverseX;
    }
};