Building Teams

#include <stdlib.h>
#include <stdint.h>
#include <stdio.h>
#include <sys/queue.h>

typedef struct node{
    int pupil;
    SLIST_ENTRY(node) entry;
} node;

SLIST_HEAD(list, node);

void rec_teamify(uint32_t n, list *graph, uint32_t *teams){
    if (teams[n] != 0){
        return;
    }
    node *cur;
    uint32_t col = 0;
    SLIST_FOREACH(cur, &graph[n], entry){
        if (teams[cur->pupil] != 0){
            if (col + teams[cur->pupil] == 3) {
                printf("IMPOSSIBLE\n");
                exit(EXIT_SUCCESS);
            }
            col = teams[cur->pupil];
        }
    }
    switch (col) {
        case 0:
            teams[n] = 1;
            break;
        case 1:
            teams[n] = 2;
            break;
        case 2:
            teams[n] = 1;
            break;

    }
    SLIST_FOREACH(cur, &graph[n], entry){
        rec_teamify(cur->pupil, graph, teams);
    }
}

void teamify(uint32_t n, list *graph, uint32_t* teams){
    rec_teamify(n, graph, teams);
    return;
}

int main() {
    uint32_t n = 0;
    uint32_t m = 1;
    if (scanf("%d %d", &n, &m) == 0)
        return EXIT_FAILURE;

    list *links = (list *) malloc(n * sizeof(list));
    for (uint32_t i = 0; i < n; i++){
        SLIST_INIT(links + i);
    }


    // graph construction

    uint32_t x, y;
    node *tmp;
    for(uint32_t i = 0; i < m; i++){
        if (scanf("%d %d", &x, &y) == 0)
            return EXIT_FAILURE;
        x--; y--;
        tmp = (node*) malloc(sizeof(node));
        tmp->pupil = y;
        SLIST_INSERT_HEAD(links + x, tmp,entry);
        tmp = (node*) malloc(sizeof(node));
        tmp->pupil = x;
        SLIST_INSERT_HEAD(links + y, tmp,entry);
    }

    uint32_t *teams = (uint32_t*) calloc(n, sizeof(uint32_t));
    for(uint32_t i = 0; i<n; i++){
        if (teams[i] == 0){
            teamify(i, links, teams);
        }
    }
    for(uint32_t i = 0; i<n; i++){
        printf("%d ", teams[i]);
    }
    printf("\n");

    return EXIT_SUCCESS;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED