7. Reverse Integer [Easy]

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.

Analyse:

利用數學方法反轉.

Solution:

class Solution {

    func reverse(_ x: Int) -> Int {
        var input = x;
        var negative = 1;
        var output = 0;

        if(input < 0) {
            input = input * -1;
            negative = -1;
        }

        whil (input > 0) {
            var value = input % 10;
            input = input / 10;

            output = output * 10 + value;
        }

        output = output * negative;

        if(output > Int32.max || output < Int32.min) {
            output = 0;
        }

        return output;
    }
}