3987. Complete Graph

#include <stdio.h>
#include <stdlib.h>

const int N = 101;

bool gr[N][N];

bool used[N];

int number = 0;

void dfs(int v)
{
    used[v] = true;
    for(int i = 0; i < N; ++i)
    {
        if(!used[i] && gr[v][i])
            dfs(i);
        number += gr[v][i];
    }

    return;
}

int main()
{
    long int n,m;
    scanf("%ld %ld",&n,&m);

    int a,b;

    for(int i = 0; i < m; ++i)
    {
        scanf("%d %d",&a,&b);
        gr[a][b] = true;
        gr[b][a] = true;
    }

    dfs(1);

    for(int i = 1; i <= n; ++i)
    {
        if(!used[i])
        {
            printf("NO");
            return 0;
        }
    }

    if(number == n*(n-1))
        printf("YES");
    else
        printf("NO");

    return 0;
}