Reverse_integer.cpp

/*Problem:
Reverse digits of an integer.

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

/*Solution:
Here are some good questions to ask before coding. Bonus points for you if you have already thought through this!
 
If the integer's last digit is 0, what should the output be? ie, cases such as 10, 100.
 
Did you notice that the reversed integer might overflow? Assume the input is a 32-bit integer, 
then the reverse of 1000000003 overflows. How should you handle such cases?

Throw an exception? Good, but what if throwing an exception is not an option? 
You would then have to re-design the function (ie, add an extra parameter).
*/

#include <stdio.h>
#include <stdlib.h>
#include <iostream>

using namespace std;

//Why need the INT_MIN be defined like that?
//Please take a look: 
//  http://stackoverflow.com/questions/14695118/2147483648-0-returns-true-in-c

#define INT_MAX     2147483647
#define INT_MIN     (-INT_MAX - 1)

int reverse(int x) {
    int y=0;
    int n;
    while( x != 0)
	{
        n = x%10;
        //Checking the over/underflow.
        //Actually, it should be y>(INT_MAX-n)/10, but n/10 is 0, so omit it.
        if (y > INT_MAX/10 || y < INT_MIN/10)
		{
             return 0;
        }
        y = y*10 + n;
        x /= 10;
    }
    return y;
}

int main()
{
    /*basic cases
    TEST(  123,  321);
    TEST( -123, -321);
    TEST( -100,   -1);
    TEST( 1002, 2001);
    //big integer
    TEST( 1463847412,  2147483641);
    TEST(-2147447412, -2147447412);
    TEST( 2147447412,  2147447412);
    //overflow
    TEST( 1000000003, 0);
    TEST( 2147483647, 0);
    TEST(-2147483648, 0);
	*/
    //customized cases
    int test = 2147483647;
	int result;
	result = reverse(test);
	cout << "result:" << result << endl;
    return 0;
}