poj1847

最短路

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#include <iostream>
#include <cstdlib>
#include <cstring>
#include <cstdio>
using namespace std;

#define INF 0x3f3f3f3f
#define N 105

int path[N], vis[N];
int cost[N][N];
int lowcost[N];
int n, a, b;

void Dijkstra(int cost[][N], int lowcost[N], int n, int beg)
{
    int i, j, min;
    memset(vis, 0, sizeof(vis));
    vis[beg] = 1;
    for (i = 0; i < n; i++)
    {
        lowcost[i] = cost[beg][i];
        path[i] = beg;
    }
    lowcost[beg] = 0;
    path[beg] = -1;
    int pre = beg;
    for (i = 1; i < n; i++)
    {
        min = INF;
        for (j = 0; j < n; j++)
            if (vis[j] == 0 && lowcost[pre] + cost[pre][j] < lowcost[j])
            {
                lowcost[j] = lowcost[pre] + cost[pre][j];
                path[j] = pre;
            }
        for (j = 0; j < n; j++)
            if (vis[j] == 0 && lowcost[j] < min)
            {
                min = lowcost[j];
                pre = j;
            }
        vis[pre] = 1;
    }
}

int main()
{
    //freopen("t.txt", "r", stdin);
    scanf("%d%d%d", &n, &a, &b);
    a--;
    b--;
    for (int i = 0; i < n; i++)
        for (int j = 0; j < n; j++)
            if (i != j)
                cost[i][j] = INF;
            else
                cost[i][j] = 0;
    for (int i = 0; i < n; i++)
    {
        int x, a;
        scanf("%d", &x);
        for (int j = 0; j < x; j++)
        {
            scanf("%d", &a);
            a--;
            if (j == 0)
                cost[i][a] = 0;
            else
                cost[i][a] = 1;
        }
    }
    Dijkstra(cost, lowcost, n, a);
    if (lowcost[b] < INF)
        printf("%d\n", lowcost[b]);
    else
        printf("-1\n");
    return 0;
}