poj1130

bfs，数据范围是10

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

#define maxn 10

int n, et;
bool map[maxn][maxn];
bool vis[maxn];
int dist[maxn];
int dist1[maxn];

void input()
{
    memset(map, 0, sizeof(map));
    scanf("%d%d", &n, &et);
    int a, b;
    while (~scanf("%d%d", &a, &b))
        map[b][a] = true;
}

void bfs(int s, int guard_room, int* dist)
{
    queue<int> q;
    memset(vis, 0, sizeof(vis));
    memset(dist, -1, sizeof(int) * n);
    vis[s] = true;
    q.push(s);
    dist[s] = 0;
    while (!q.empty())
    {
        int u = q.front();
        q.pop();
        for (int i = 0; i < n; i++)
            if (map[u][i] && !vis[i] && i != guard_room)
            {
                q.push(i);
                vis[i] = true;
                dist[i] = dist[u] + 1;
            }
    }
}

int work()
{
    int ret = 0;
    for (int i = 1; i < n; i++)
        if (i != et)
        {
            bfs(et, i, dist1);
            if (dist1[0] != -1)
                continue;
            if (dist[ret] > dist[i])
                ret = i;
        }
    return ret;
}

int main()
{
    //freopen("t.txt", "r", stdin);
    input();
    bfs(et, -1, dist);
    printf("Put guards in room %d.\n", work());
    return 0;
}