7. 整数反转

func reverse(x int) int {
    MIN := -2147483648
    MAX := 2147483647
    var res int
    for x != 0 {
        y := x % 10
        if res < (MIN - y) / 10 || res > (MAX - y) / 10 {
            return 0
        }
        x = x / 10
        res = res * 10 + y
    }
    return res
}