http://acm.hdu.edu.cn/showproblem.php?pid=5253

Prim算法是

1.每次選出 （已經選出的）點集 能夠連接 邊權值最小的點

2.使用新找出的點能帶來的新的更小的邊權，來更新舊的較大的邊權

3.重復，直到連接所有點

的貪心算法

使用優先權隊列優化 查找 邊權值最小的點 的步驟。

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <iostream>
#include <vector>
#include <queue>
#include 
 
<algorithm>
using namespace std;
typedef long long LL;
typedef pair<int,int> P;
int cnt;
int t,n,m;
int mp[1005][1005];
bool vis[1005][1005];
int dirx[] = {0,1,0,-1};
int diry[] = {1,0,-1,0};

LL bfs()
{
    priority_queue<P, vector<P>, greater<P> > pq;
    while(!pq.empty()) pq.pop();
    memset(vis, 
 
0, sizeof(vis));
    pq.push(P(0, 0));
    LL cost = 0;
    int cnt = 0;
    while(!pq.empty())
    {
        P p = pq.top();
        pq.pop();
        int val = p.first, id = p.second;
        int x = id/m, y = id%m;
        if(vis[x][y]) continue;
        vis[x][y] = 1;
        cost += val;
        for(int
 
 i = 0; i < 4; i++)
        {
            int nx = x + dirx[i], ny = y + diry[i];
            if(nx < 0 || ny < 0 || nx >= n || ny >= m || vis[nx][ny]) continue;
            int nval = abs(mp[x][y] - mp[nx][ny]), nid = nx*m+ny;
            pq.push(P(nval, nid));
        }
        cnt++;
        if(cnt >= m*n) break;
    }
    return cost;
}

int main()
{
    scanf("%d", &t);
    while(t--)
    {
        scanf("%d%d", &n,&m);
        for(int i = 0; i < n; i++)
        {
            for(int j = 0; j < m; j++)
            {
                scanf("%d", &mp[i][j]);
            }
        }
        static int kase = 0;
        printf("Case #%d:\n%lld\n", ++kase, bfs());
    }
    return 0;
}

HDU 5253 Prim算法