CFR 300 B. Coach ( DFS )

Problem - 300B - Codeforces
暴力でやるだけ。実装が下手。
つまらないミスで時間を溶かした。

#include <bits/stdc++.h>
using namespace std;
const int MAXN = 48 + 2;
const int MAXM = MAXN * MAXN / 2;

int n, m;
vector< int > G[ MAXN ];

struct UnionFind{
    int fa[ MAXN ];
    void init( int _n ){
        for( int i = 1; i <= _n; ++i )
            fa[ i ] = i;
    }
    int find( int x ){ return fa[ x ] == x ? x : fa[ x ] = find( fa[ x ] ); }
    bool unite( int a, int b ){
        int x = find( a );
        int y = find( b );
        if( x == y ) return false;
        fa[ x ] = y; return true;
    }
} uf;

int vis[ MAXN ];

void dfs( int u ){
    vis[ u ] = 1;
    for( int v : G[ u ] ){
        int x = uf.find( u );
        int y = uf.find( v );
        if( x != y ){
            uf.unite( u, v );
            dfs( v );
        }
    }
}

void solve(){
    uf.init( n );
    for( int u = 1; u <= n; ++u )
        if( !vis[ u ] )
            dfs( u );
    vector< int > team[ MAXN ];
    for( int u = 1; u <= n; ++u ){
        int x = uf.find( u );
        team[ x ].push_back( u );
        if( team[ x ].size() > 3 ) return (void)puts("-1");
    }
    vector< int > v1, v2, v3;
    for( int u = 1; u <= n; ++u ){
        if( team[ u ].size() == 1 )
            v1.push_back( team[ u ][ 0 ] );
        if( team[ u ].size() == 2 )
            v2.push_back( team[ u ][ 0 ] ), v2.push_back( team[ u ][ 1 ] );
        if( team[ u ].size() == 3 )
            v3.push_back( team[ u ][ 0 ] ), v3.push_back( team[ u ][ 1 ] ), v3.push_back( team[ u ][ 2 ] );
    }
    // printf("%d %d %d\n", v1.size(), v2.size(), v3.size());
    if( v2.size() / 2 > v1.size() ) return (void)puts("-1");
    for( int i = 0; i < v2.size(); i += 2 )
        printf("%d %d %d\n", v2[ i ], v2[ i + 1 ], v1[ i / 2 ]);
    for( int i = v2.size() / 2; i < v1.size(); i += 3 )
        printf("%d %d %d\n", v1[ i ], v1[ i + 1 ], v1[ i + 2 ]);
    for( int i = 0; i < v3.size(); i += 3 )
        printf("%d %d %d\n", v3[ i ], v3[ i + 1 ], v3[ i + 2 ]);
}

int main(){
    scanf("%d%d", &n, &m);
    for( int i = 0; i < m; ++i ){
        int u, v; scanf("%d%d", &u, &v);
        G[ u ].push_back( v );
        G[ v ].push_back( u );
    }
    solve();
    return 0;
}