Reverse Integer

Question

• leetcode: Reverse Integer | LeetCode OJ
• lintcode: (413) Reverse Integer

Problem Statement

Reverse digits of an integer. Returns 0 when the reversed integer overflows (signed 32-bit integer).

Example

Given x = 123, return 321

Given x = -123, return -321
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.

Note:
The input is assumed to be a 32-bit signed integer. Your function should return 0 when the reversed integer overflows.

题解

如题目中所提示的，要考虑一下溢出的处理。

C++

class Solution {
public:
    int reverse(int x) {
        const int min = 0x80000000; 
        const int max = 0x7FFFFFFF;
        long s = 0;

        while(x != 0){
            if (x >= min && x <= max){
                int temp = x % 10;
                s = s * 10 + temp;
                x = (x - temp) / 10;
                if(s < min || s > max){
                    s = 0;
                    break;
                } 
            }
            else{
                s = 0;
                break;
            }
        }
        return s;
    }
};

Error分析：

Error

当执行到s = 964632435，此时还没有溢出，如果继续s * 10 + temp，此时s肯定会溢出，因此会报错。因此增加了一个判断s是否溢出。
32位int范围:-2147483648～2147483647。