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/* roid_objs is an array of asteroids that keeps track of all the roids */
typedef struct {
        roid_t * roid1;
        roid_t * roid2;
} roid_roid_collisions_t;

int n, i, j;
int ASTEROID_COUNT;
roid_roid_collisions_t * poss_roid_colls;

ASTEROID_COUNT = 5;
n = ASTEROID_COUNT*(ASTEROID_COUNT-1)*0.5;
poss_roid_colls = calloc(n, sizeof(roid_roid_collisions_t));
n = 0;

for( i=0; i < ASTEROID_COUNT; i++ ){
        for( j=i; j < ASTEROID_COUNT; n++, j++) {
                poss_roid_colls[n].roid1 = &roid_objs[i];
                poss_roid_colls[n].roid1 = &roid_objs[j];
        }
}

/*
Math:
for 5 roids the possible collisions are:
12345
2345
345
45
5
*/