#include <stdlib.h>
/*
 * Check if two queens (row1,col1) and (row2,col2) attack each other.
 *
 * Two pieces are on the same diagonal if 
 * the difference of their rows == +- difference of their columns
 *
 */
int attack(int row1, int col1, int row2, int col2)
{
    return(row2 == row1 || col1 == col2 || abs(row2 - row1) == abs(col1 - col2));
}