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input/code.cpp: In function 'void Test()':
input/code.cpp:51:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   51 |     freopen("temp\\in.txt", "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
input/code.cpp: In function 'int main()':
input/code.cpp:57:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   57 |     scanf("%d%d", &n, &m);
      |     ~~~~~^~~~~~~~~~~~~~~~
input/code.cpp:65:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   65 |         scanf("%d%d", &a, &b);
      |         ~~~~~^~~~~~~~~~~~~~~~

#include<iostream>
#include<cstdio>
#include<algorithm>
typedef long long LL;

const int N=100005, M=400005;

int head[N], nxt[M], to[M], cnt, mark[N];
bool vis[N], fail_flag;


void Add(int u, int v) {
  nxt[++cnt] = head[u]; 
  head[u] = cnt;        
  to[cnt] = v;       
}

bool DFS(int u, int father)
{
    if(father == 0)
        mark[u] = 1;
    int son_mark = 2;
    if(mark[u] == 2)
        son_mark = 1; 
    
    for (int i = head[u]; ~i; i = nxt[i]) 
    {
        int v = to[i];

        if(v == father)
            continue;

        if(vis[v] && mark[v]!=son_mark)
        {
            fail_flag = true;
            break;
        } else {
            vis[v] = true;
            mark[v] = son_mark;
            if(!DFS(v, u))
                break;
        }
    }

    return !fail_flag;
}


void Test()
{
    freopen("temp\\in.txt", "r", stdin);
}
int main()
{
    // Test();
    int n, m;
    scanf("%d%d", &n, &m);
 
    for(int i=1; i<=n; i++)
        head[i] = -1;

    for(int i=1; i<=m; i++)
    {
        int a, b;
        scanf("%d%d", &a, &b);
        Add(a, b);
        Add(b, a);
    }

    for(int i=1; i<=n; i++)
    {
        if(!vis[i] && !DFS(i, 0))
            break;
    }

    if(fail_flag)
        printf("IMPOSSIBLE");
    else
        for(int i=1; i<=n; i++)
            printf("%d ", mark[i]);
    return 0;
}

Test 1

Verdict: RUNTIME ERROR

Test 2

Verdict: RUNTIME ERROR

Test 3

Verdict: RUNTIME ERROR

Test 4

Verdict: RUNTIME ERROR

Test 5

Verdict: ACCEPTED

Test 6

Verdict: RUNTIME ERROR

Test 7

Verdict: RUNTIME ERROR

Test 8

Verdict: RUNTIME ERROR

Test 9

Verdict: RUNTIME ERROR

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED