usaco 2.3 concom...

/*
    ID:chenjiong
    PROG:concom
    LANG:C++
*/

#include <stdio.h>
#include <string.h>

const int MAXN = 101;

int map[MAXN][MAXN];
bool con[MAXN][MAXN];
int E;
bool flag;

int cal()
{
    int i,j;
    int sum = 0;
    for ( i = 0; i < MAXN; i++)
        for ( j = 0; j < MAXN; j++)
            if ( con[i][j] )
                sum += 1;
    return sum;
}

void init()
{
    flag = true;
    memset(map,0,sizeof(map));

    int i,j,v;
    scanf("%d",&E);
    while ( E-- )
    {
        scanf("%d%d%d",&i,&j,&v);
        map[i][j] = v;
    }
}

void solve()
{
    int i,j,k;
    memset(con,0,sizeof(con));

    for ( i = 0; i < MAXN; i++)
        con[i][i] = true;

    for ( i = 0; i < MAXN; i++)
        for ( j = 0; j < MAXN; j++)
            if ( map[i][j] > 50 )
                con[i][j] = true;

    int pre = cal();

    while ( true)
    {
        for ( i = 0; i < MAXN; i++)
        {
            for ( j = 0; j < MAXN; j++)
            {
                int sum = 0;
                for ( k = 0; k < MAXN; k++)
                {    
                    if ( con[i][k] )
                        sum += map[k][j];
                }        
                if ( sum > 50 )
                    con[i][j] = true;
            }
        }
        if ( pre == cal() )
            break;
        else 
            pre = cal();
    }
}

void print()
{
    int i,j;
    for ( i = 0; i < MAXN; i++)
    {
        for ( j = 0; j < MAXN; j++)
        {
            if ( con[i][j] && i != j )
                printf("%d %d\n",i,j);
        }
    }
}

int main()
{
    freopen("concom.in","r",stdin);
    freopen("concom.out","w",stdout);

    init();
    solve();
    print();
    return 0;
}