Kruskal算法

Posted 2020-12-19 cyl-oi-miracle

#include <bits/stdc++.h>
#define MAXN 200005
using namespace std;
int node,edge,ans=0,k=0;		
int fat[MAXN],siz[MAXN];					
struct EDGE
{
	int from,to,cost;
}	e[MAXN];
bool cmp(EDGE a,EDGE b)	{return a.cost<b.cost;}
int Find(int x){ return (fat[x]==x)? x : fat[x]=Find(fat[x]); }	//查 
void unionn(int x,int y)//并 
{
	x=Find(x); y=Find(y);
	if(siz[x]>siz[y])	swap(x,y);
	fat[x]=y;	siz[y]+=siz[x]; 
}
bool kruskal()
{
	sort(e+1,e+edge+1,cmp);
	//贪心，排序 
	for(int i=1;i<=edge;++i)
	{
		if(k==node-1) break;
		if(Find(e[i].from) != Find(e[i].to))
		{
			unionn(e[i].from,e[i].to); 
			ans+=e[i].cost;	++k; 
		}
	}
	return (k==node-1);
}
int main()
{
	scanf("%d%d",&node,&edge);
	//node点数，edge边数 
	for(int i=1;i<=edge;++i)	scanf("%d%d%d",&e[i].from,&e[i].to,&e[i].cost);
	//邻接矩阵 
	for(int i=1;i<=node;++i)	{fat[i]=i;siz[i]=1;}
	//初始化 
	if(kruskal())	printf("%d",ans);
	return 0;
}