題目（來自leetcode網站）：

題目的意思是把 輸入的整數倒敘輸出，不改變符號，且需要對整數的範圍進行判斷；

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 store integers within the 32-bit signed integer range: [−2^31,  2^31 − 1]. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

解答：

#PYTHON版本
class Solution:
    def reverse(self, x):
        """
        :type x: int
        :rtype: int
        """
        if x <-2**31 or x >(2**31) -1:
            return 0
        else:
            b = -int(str(x)[::-1][:-1]) if x <0 else int(str(x)[::-1])
            if b <-2**31 or b >(2**31) -1:
                return 0
            else:
                return b
        
#C++版本
#inlude<cstring>
#include <sstream>
class Solution {
public:
    int reverse(int x) {
        int result=0;
        if(x < pow(-2,31) || x >pow(2,31)-1){
            return 0;
        }
        else{
            string s=to_string(x);
            x>=0? s=s.substr(0,s.size()) : s=s.substr(1,s.size()-1);
            s=reverse_str(s);
            stringstream ss;
            ss<<s;
            ss>>result;
            x>=0? result:result=0-result;
            if(result ==pow(2,31)-1 ||result==pow(-2,31)+1){
                return 0;
            }else{
                return result;
            }
        }
            
    }
    string reverse_str(string s){
        string b;
        for(int i=0;i<s.size();i++){
            b+=s[s.size()-1-i];
        }
        return b;
    }
};