7. Reverse Integer

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.

Solution

(1) Java

Only pay attention to overflow when reverse

public int reverse(int x) {
        if (x == 0) {
            return x;
        }
        int sign = x > 0 ? 1 : -1;
        int rst = 0;
        x = Math.abs(x);
        while (x > 0) {
            if (rst*10/10 != rst) {
                return 0;
            }
            rst = rst*10+x%10;
            x = x/10;
        }
        return rst*sign;
    }

(2) Python

Use extend slice method for string

def reverse(self, x):
        """
        :type x: int
        :rtype: int
        """
        sign = cmp(x, 0)
        rst = int(str(sign*x)[::-1])
        return rst*sign if rst < 2**31-1 else 0

(3) Scala

Recursion of course, still pay attention to overflow

object Solution {
    def reverse(x: Int): Int = {
        val sign = if (x >= 0) 1 else -1
        val rst = helper(sign*x, 0) 
        return if (rst > Int.MaxValue) 0 else sign*rst
    }

    def helper(x: Int, rst: Int): Int = {
        if (x == 0) {
            return rst
        }
        if (rst*10/10 != rst) {
            return 0
        }
        return helper(x/10, rst*10+x%10)      
    }
}