hdoj 畅通工程 没有最短路的情况

#include <iostream>
#include <memory.h>
using namespace std;
const int IN = (1<<28);
int N,M,S,T;
int G[205][205];
int dist[205];
int visited[205];
void dij()
{
    for( int i = 1; i <= N; i++ )
        dist[i] = G[S+1][i];
    visited[S+1] = 1;
    while( 1 )
    {
        int MinV = 0,Min = IN;
        for( int i = 1; i <= N; i++ )
        {
            if( !visited[i] && dist[i] < Min )
            {
                Min = dist[i];
                MinV = i;
            }
        }
        if( !MinV )
            break;
        else
        {
            visited[MinV] = 1;
            for( int i = 1; i <= N; i++ )
            {
                if( !visited[i] && dist[i] > dist[MinV] + G[MinV][i])
                    dist[i] = dist[MinV] + G[MinV][i];
            }
        }
    }
}
int main()
{
    while( cin >> N >> M )
    {
        memset(dist, 0, sizeof(dist));
        memset(G, 0, sizeof(G));
        memset(visited, 0, sizeof(visited));
        for( int i = 1; i <= N; i++ )
            for( int j = 1; j <= N; j++ )
            {
                if( i==j )
                {
                    G[i][j] = 0;
                }
                else
                    G[i][j] = IN;
            }
        while( M-- )
        {
            int Begin,End,Length;
            cin >> Begin >> End >> Length;
            if( Length <= G[Begin+1][End+1] )
            {
            G[Begin+1][End+1] = Length;
            G[End+1][Begin+1] = Length;
            }
        }
        cin >> S >> T;
        dij();
        if( dist[T+1] != IN )
            cout << dist[T+1] << endl;
        else
            cout << -1 << endl;
    }
    return 0;
}