poj1130

bfs，数据范围是10

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#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;

}