[leetcode][大数] Reverse Integer

题目：

Reverse digits of an integer.

Example1: x = 123,return 321
Example2: x = -123,return -321

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Have you thought about this?

Here are some good questions to ask before coding. Bonus points for you if you have already thought through this!

If the integer's last digit is 0,what should the output be? ie,cases such as 10,100.

Did you notice that the reversed integer might overflow? Assume the input is a 32-bit integer,then the reverse of 1000000003 overflows. How should you handle such cases?

For the purpose of this problem,assume that your function returns 0 when the reversed integer overflows.

Update (2014-11-10):
Test cases had been added to test the overflow behavior.

class Solution {
public:
    int reverse(int x) {
        long long res = 0;//考虑到大数问题，res的类型用long long 而非 int
        while(x){
            res = res * 10 + x % 10;
            x /= 10;
        }
        // res为正数或负数分开讨论，超过int的表示范围就返回0
        if(res < 0) res = res < INT_MIN ? 0 : res; 
        else res = res > INT_MAX ? 0 : res;
        return res;
    }
};