洛谷 P3366 【模板】最小生成树

目录

• $code$

---

题目

戳

思路

最小生成树
$\text{prim}$和$\text{kruskal}$

$code$

$\text{prim}$

/*
prim+链式前向星
*/
#include<bits/stdc++.h>
#define maxn 5001
#define inf 1061109567
using namespace std;
int n,m,cnt,ans;
int dis[maxn],head[maxn];
bool vis[maxn];
struct edge{
    int next,to,w;
}edge[200001<<1];
inline int read(){
    int x=0;bool f=0;char c=getchar();
    while(c<'0'||c>'9'){if(c=='-')f=!f;c=getchar();}
    while(c>='0'&&c<='9'){x=x*10+c-'0';c=getchar();}
    return f?-x:x;
}
inline void addedge(int from,int to,int w){
    edge[++cnt].to=to,edge[cnt].next=head[from];
    edge[cnt].w=w,head[from]=cnt;
}
void prim(){
    int tot=0,k=1;
    dis[1]=0;
    for(int i=head[1];i;i=edge[i].next){
        if(dis[edge[i].to]>edge[i].w)
            dis[edge[i].to]=edge[i].w;
    }
    while(++tot<n){
        int sum=0x7fffffff;
        vis[k]=1;
        for(int i=1;i<=n;++i){
            if(!vis[i]&&dis[i]<sum){
                k=i;
                sum=dis[i];
            }
        }
        ans+=sum;
        for(int i=head[k];i;i=edge[i].next){
            if(!vis[edge[i].to]&&dis[edge[i].to]>edge[i].w)
                dis[edge[i].to]=edge[i].w;
        }
    }
}

int main(){
    memset(dis,0x3f3f3f,sizeof(dis));
    n=read(),m=read();
    int u,v,w;
    while(m--){
        u=read(),v=read(),w=read();
        addedge(u,v,w),addedge(v,u,w);
    }
    prim();
    for(int i=1;i<=n;++i){
        if(dis[i]==inf){
            printf("orz\n");
            return 0;
        }
    }
    printf("%d\n",ans);
    return 0;
}

/*
prim+邻接矩阵
*/
#include<iostream>
#include<cstring>
#include<string>
#include<cstdio>
#include<algorithm>
#define maxn 5001
#define inf 1061109567
using namespace std;
int n,m,ans;
int map[maxn][maxn],dis[maxn];
bool vis[maxn];
inline int read(){
    int x=0;bool f=0;char c=getchar();
    while(c<'0'||c>'9'){if(c=='-')f=!f;c=getchar();}
    while(c>='0'&&c<='9'){x=x*10+c-'0';c=getchar();}
    return f?-x:x;
}
void prim(){
    dis[1]=0;
    for(int i=1;i<=n;++i){
        int k=0;
        for(int j=1;j<=n;++j){
            if(!vis[j]&&dis[k]>dis[j]) k=j;
        }
        vis[k]=1;
        for(int j=1;j<=n;++j){
            if(!vis[j]&&map[k][j]<dis[j])
                dis[j]=map[k][j];
        }
    }
}

int main(){
    memset(map,0x3f3f3f,sizeof(map));
    memset(dis,0x3f3f3f,sizeof(dis));
    n=read(),m=read();
    int u,v,w;
    for(int i=1;i<=m;++i){
        u=read(),v=read(),w=read();
        if(map[u][v]>w){
            map[u][v]=w;
            map[v][u]=w;
        }
    }
    prim();
    for(int i=1;i<=n;++i){
        ans+=dis[i];
        if(dis[i]==inf){
            printf("orz\n");
            return 0;
        }
    }
    printf("%d\n",ans);
    return 0;
}