# \[LeetCode] 7. Reverse Integer \[Easy] \[LeetCode]

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: \[−231,  231 − 1]. 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:**

```swift
class Solution {

    func reverse(_ x: Int) -> Int {
        var input = x;
        var negative = 1;
        var output = 0;
        
        if(input < 0) {
            input = input * -1;
            negative = -1;
        }
        
        while(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;
    } 
}
```