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// Source : https://oj.leetcode.com/problems/reverse-integer/

// Author : Hao Chen

// Date : 2014-06-18

/**********************************************************************************

* Reverse digits of an integer.

* Example1: x = 123, return 321

* Example2: x = -123, return -321

* Have you thought about this?

* 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>

//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;

}

#define TEST(n, e) printf("%12d => %-12d %s!\n", n, reverse(n), e == reverse(n)?"passed":"failed")

int main(int argc, char**argv)

{

//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

if (argc<2){

return 0;

}

printf("\n");

for (int i=1; i<argc; i++) {

int n = atoi(argv[i]);

printf("%12d => %-12d %s!\n", n, reverse(n), reverse(reverse(n))==n ? "passed":"failed");

}

return 0;

}

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