Hdu1102 Constructing Roads 【最小生成树】

http://acm.hdu.edu.cn/showproblem.php?pid=1102

Prim算法解决最短路问题

 

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <cmath>
#include <queue>
using namespace std;
template <class T> void checkmin(T &t,T x) {if(x < t) t = x;}
template <class T> void checkmax(T &t,T x) {if(x > t) t = x;}
template <class T> void _checkmin(T &t,T x) {if(t==-1) t = x; if(x < t) t = x;}
template <class T> void _checkmax(T &t,T x) {if(t==-1) t = x; if(x > t) t = x;}
typedef pair <int,int> PII;
typedef pair <double,double> PDD;
typedef long long ll;
#define foreach(it,v) for(__typeof((v).begin()) it = (v).begin(); it != (v).end ; it ++)
void checkmin(int &a,int b) { if(b < a) a = b; }
void checkmax(int &a,int b) { if(b > a) a = b; }
const int N = 111 , M = 22222;
int dist[N] , n , m;
bool vis[N];
queue <int > q;
#define inf (1<<29)
struct Edge {
    int v , w , next;
    Edge () {}
    Edge(int v,int w,int next) : v(v),w(w),next(next) {}
}edge[M];
int E , head[N];
void init() {
    E = 0; memset(head,-1,sizeof(head));
}
void addedge(int u,int v,int w) {
    edge[E] = Edge(v,w,head[u]);
    head[u] = E++;
    edge[E] = Edge(u,w,head[v]);
    head[v] = E++;
}
void prim() {
    int ans = 0;
    for(int i=1;i<=n;i++) dist[i] = inf , vis[i] = 0;
    dist[1] = 0;
    while(1) {
        int u = -1 , Min = inf;
        for(int i=1;i<=n;i++) {
            if(!vis[i] && (u==-1 || dist[i] < Min) ) {
                Min = dist[i] ; u = i;
            }
        }
        if(u == -1) break;
        vis[u] = 1;
        ans += dist[u];
        for(int i=head[u];i!=-1;i=edge[i].next) {
            int v = edge[i].v;
            if(!vis[v]) checkmin(dist[v] , edge[i].w);
        }
    }
    printf("%d\n" , ans);
}
int main() {
    while(~scanf("%d",&n)) {
        init();
        for(int i=1;i<=n;i++)
        for(int j=1;j<=n;j++) {
            int w;
            scanf("%d",&w);
            if(i < j) addedge(i , j , w);
        }
        scanf("%d",&m);
        while(m --) {
            int u , v;
            scanf("%d%d",&u,&v);
            addedge(u , v , 0);
        }
        prim();
    }
    return 0;
}