hdu 4856 Tunnels BFS+不回起点的TSP

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=4856

 

注意到隧道是单向的

bfs求出距离以后套用TSP模板即可

 

注意日本人那本白书上的模板是最后要回到起点的

而本题并不回起点

具体的做法是建一个超级起点，跟图中每一个点都建花费为0的边，然后以之为起点跑一边即可

 

#include <cstring>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <cstdio>
#include <stack>
#include <vector>
#include <queue>
#include <map>
#include <set>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> P;

const int maxn = 17;
const int INF = 0x3f3f3f3f;

int n, m;
char a[maxn][maxn];
int b[maxn][2];
int c[maxn][2];
int d[maxn][maxn];

int dp[1 << maxn][maxn];

const int walk[][2] = {1, 0, 0, 1, -1, 0, 0, -1};

struct Node
{
    int x, y;
    int s;
};

bool vis[maxn][maxn];
void bfs(int u, int v)
{
    memset(vis, 0, sizeof(vis));
    queue<Node> que;
    Node cur;

    cur.x = c[u][0];
    cur.y = c[u][1];
    cur.s = 0;

    vis[cur.x][cur.y] = 1;
    que.push(cur);

    while(!que.empty())
    {
        cur = que.front();
        que.pop();
        int x = cur.x;
        int y = cur.y;

        if(x == b[v][0] && y == b[v][1])
        {
            d[u][v] = cur.s;
            return;
        }

        for(int i = 0; i < 4; i++)
        {
            int nx = x + walk[i][0];
            int ny = y + walk[i][1];

            if(0 <= nx && nx < n && 0 <= ny && ny < n && a[nx][ny] == '.' && vis[nx][ny] == 0)
            {
                vis[nx][ny] = 1;
                Node nxt = {nx, ny, cur.s+1};
                que.push(nxt);
            }
        }
    }

    d[u][v] = INF;
    return;
}

int main()
{
    //freopen("in.txt", "r", stdin);

    while(scanf("%d%d", &n, &m) == 2)
    {
        for(int i = 0; i < n; i++)
            scanf("%s", a[i]);

        for(int i = 0; i < m; i++)
        {
            scanf("%d%d%d%d", &b[i][0], &b[i][1], &c[i][0], &c[i][1]);

            b[i][0]--;
            b[i][1]--;
            c[i][0]--;
            c[i][1]--;
        }

        for(int i = 0; i < m; i++)
            for(int j = 0; j < m; j++)
            {
                if(i == j)
                    continue;

                bfs(i, j);
                bfs(j, i);
            }

        for(int i = 0; i <= m; i++)
            d[i][i] = INF;

        for(int i = 0; i < m; i++)
            d[i][m] = d[m][i] = 0;

        int ans = INF;

        m++;

        for(int i = 0; i < 1 << m; i++)
            fill(dp[i], dp[i] + m, INF);

        dp[((1 << m) - 1)][m-1] = 0;

        for(int S = (1 << m) - 1; S >= 0; S--)
            for(int v = 0; v < m; v++)
                for(int u = 0; u < m; u++)
                    if(!(S >> u & 1))
                    {
                        dp[S][v] = min(dp[S][v], dp[S | 1 << u][u] + d[v][u]);
                        /*if(S == 0 && dp[S][v] < minnum)
                            minnum = dp[S][v];*/
                    }

        if(dp[0][m-1] != INF)
            printf("%d\n", dp[0][m-1]);
        else
            printf("-1\n");
    }

    return 0;
}