POJ 3026 Borg Maze(bfs + prime)

解题思路:

先用BFS预处理出每个字母节点到其它节点的最短路径,然后套用prime算法。

#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <algorithm>
#include <queue>
#include <stack>
#include <vector>
#include <set>
#include <map>
#define LL long long
using namespace std;
const int MAXN = 100 + 10;
char G[MAXN][MAXN];
int A[MAXN][MAXN];
int N, M;
int g[][2] = {{-1,0},{1,0},{0,-1},{0,1}};
int cost[MAXN][MAXN];
int t[MAXN][MAXN];
void bfs(int sx, int sy)
{
	memset(t, -1, sizeof(t));
	queue<pair<int,int> > Q;
	Q.push(make_pair(sx,sy));
	t[sx][sy] = 0;
	while(!Q.empty())
	{
		pair<int,int> u = Q.front();
		Q.pop();
		if(A[u.first][u.second] != -1)
		{
			cost[A[sx][sy]][A[u.first][u.second]] = t[u.first][u.second];
		}
		for(int i=0;i<4;i++)
		{
			int x = u.first + g[i][0];
			int y = u.second + g[i][1];
			if(G[x][y] == '#' || t[x][y] != -1)
				continue;
			t[x][y] = t[u.first][u.second] + 1;
			Q.push(make_pair(x,y));
		}
	}
}
const int INF = 0x3f3f3f3f;
bool vis[MAXN];
int lowc[MAXN];
int prime(int n)
{
	int ans = 0;
	memset(vis, 0, sizeof(vis));
	vis[0] = true;
	for(int i=1;i<n;i++) lowc[i] = cost[0][i];
	for(int i=1;i<n;i++)
	{
		int minc = INF;
		int p = -1;
		for(int j=0;j<n;j++)
		{
			if(!vis[j] && minc > lowc[j])
			{
				minc = lowc[j];
				p = j;
			}
		}
		if(minc == INF) return -1;
		ans += minc;
		vis[p] = true;
		for(int j=0;j<n;j++)
		{
			if(!vis[j] && lowc[j] > cost[p][j])
				lowc[j] = cost[p][j];
		}
	}
	return ans;
}
int main()
{
	int T;
	scanf("%d", &T);
	while(T--)
	{
		scanf("%d%d", &M, &N);
		gets(G[0]);
		int tot = 0;
		for(int i=0;i<N;i++)
			gets(G[i]);
		/*for(int i=0;i<N;i++)
		{
			for(int j=0;j<M;j++)
				cout<<G[i][j];
			cout<<endl;
		}*/
		memset(A, -1, sizeof(A));
		for(int i=0;i<N;i++)
		{
			for(int j=0;j<M;j++)
			{
				if(G[i][j] == 'S' || G[i][j] == 'A')
					A[i][j] = tot++;
			}
		}
		for(int i=0;i<N;i++)
		{
			for(int j=0;j<M;j++)
			{
				if(A[i][j] != -1)
					bfs(i, j);
			}
		}
		int ans = prime(tot);
		printf("%d\n", ans);
	}
	return 0;
}
		
时间: 2024-10-13 10:07:40

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