[Leetcode 14] 7 Reverse Integer

Problem:

Reverse digits of an integer.

Example1: x = 123, return 321
Example2: x = -123, return -321

Analysis:

It's the basic conversion problem. The only thing to note is that keep the negative number as negative and positive as positive.

 

Code:

public class Solution {
    public int reverse(int x) {
        // Start typing your Java solution below
        // DO NOT write main() function
        int rx = 0;
        boolean isNegative = (x<0)? true : false;
        
        if (isNegative)
            x = -x;
        
                
        while (x > 0) {
            rx = rx*10 + x%10;
            x /= 10;
        }
        
        return isNegative? -rx : rx;
    }
}

Here is a simplified version of the code

public class Solution {
    public int reverse(int x) {
        // Start typing your Java solution below
        // DO NOT write main() function
        int res = 0;
        
        while (x != 0) {
            res = res * 10 + x % 10;
            x /= 10;
        }
        
        return res;
    }
}

 

Attention:

As the Spoiled Information mentioned, there are many problems to consider before starting to code.

The first thing is how to deal with negative numbers?

The second thing is how to deal with numbers ending with 0, e.g. 10, 100, 1000, should the reversed number be 01 or 1?

Finally, the biggest problem is overflow after reversing, example is that for a signed 32bit integer 1000000003, the reversed integer is 3000000001, which exceeds the maximum value of signed 32-bit integer - 2147483647. One possible way to handle it is adding a isValid flag to notify user whether the returned result is valid