7.Reverse Integer (INT; Overflow)

Reverse digits of an integer.

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

 

思路：要注意溢出。用以下做法，会溢出。

class Solution {
public:
    int reverse(int x) {
        int ret = 0;
        while(x){
            ret = ret * 10 + x%10;
            x /= 10;
        }
        return ret;
    }
};

改进的做法：

class Solution {
public:
    int reverse(int x) {
        if (x == INT_MIN) return 0;
        
        int ret = 0;
        int digit;
        bool pos = x>=0?true:false;
        
        x = abs(x); //现在对负数求模编译器不统一，所以转为正数操作
        while(x){
            digit = x%10;
          
            if (ret > (INT_MAX - digit) / 10)  //10*ret+digit > INT_MAX
                return 0;
  
            ret = ret * 10 + digit;
            x /= 10;

        }
        if(pos) return ret;
        else return (-ret);

    }
};