poj1258 Agri-Net （prim+heap）

题目链接：poj1258 Agri-Net

这题我上个月做过，是个大水题，今天看见有人用prim+heap做的，就学习了下。

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
#include<vector>
#include<set>
#define CLR(a,b) memset((a),(b),sizeof((a)))
using namespace std;

const int inf = 0x3f3f3f3f;
const int N = 101;
int low[N], s[N];
int n, ans, num;
struct Edge{
    int v,c;
    Edge(int _v=0,int _c=0):v(_v),c(_c){}
    bool operator < (const Edge&r)const{
        return r.c < c;
    }
};
vector<Edge>g[N];

int prim_heap(){
    priority_queue<Edge>q;
    int i, u, v, w;
    Edge p;
    ans = 0;//最小生成树总权值
    num = 0;//已加入最小生成树的顶点数目
    q.push(Edge(0, 0));
    while(!q.empty() && num < n){
        p = q.top(); q.pop();
        u = p.v;
        if(s[u]) continue;
        s[u] = 1;
        ans += p.c;
        num++;
        for(i = 0; i < g[u].size(); ++i){
            v = g[u][i].v;
            if(s[v] == 0){
                w = g[u][i].c;
                if(w < low[v]){
                    low[v] = w;
                    q.push(Edge(v, w));
                }
            }
        }
    }
    if(num < n)
        return -1;
    return ans;
}
int main(){
    int i, j, x;
    while(scanf("%d", &n) == 1){
        for(i = 0; i < n; ++i)
            g[i].clear();
        for(i = 0; i < n; ++i)
            for(j = 0; j < n; ++j){
                scanf("%d", &x);
                g[i].push_back(Edge(j, x));
        }
        CLR(s, 0); CLR(low, inf);
        printf("%d\n",prim_heap());
    }
    return 0;
}