BZOJ 3732: Network Kruskal 重构树

模板题，练练手~

Code:

#include <cstdio>
#include <algorithm>
#define N 80000
#define setIO(s) freopen(s".in","r",stdin)
using namespace std;
namespace tree {
	int hd[N],to[N],nex[N],edges;
	int fa[N],top[N],siz[N],dep[N],son[N];
	void addedge(int u,int v) {
		nex[++edges]=hd[u],hd[u]=edges,to[edges]=v;
	}
	void dfs1(int u,int ff) {
		fa[u]=ff,siz[u]=1,dep[u]=dep[ff]+1;
		for(int i=hd[u];i;i=nex[i])
			if(to[i]!=ff) {
				dfs1(to[i],u),siz[u]+=siz[to[i]];
				if(siz[to[i]]>siz[son[u]]) son[u]=to[i];
			}
	}
	void dfs2(int u,int tp) {
		top[u]=tp;
		if(son[u]) dfs2(son[u],tp);
		for(int i=hd[u];i;i=nex[i])
			if(to[i]!=son[u]&&to[i]!=fa[u])
				dfs2(to[i],to[i]);
	}
	int LCA(int x,int y) {
		while(top[x]!=top[y])
			dep[top[x]]>dep[top[y]]?x=fa[top[x]]:y=fa[top[y]];
		return dep[x]<dep[y]?x:y;
	}
};
struct Edge {
	int u,v,c;
}e[N];
bool cmp(Edge a,Edge b) {
	return a.c<b.c;
}
int p[N],maxv[N],n,m,k,tot;
int find(int x) {
	return p[x]==x?x:p[x]=find(p[x]);
}
int main() {
	int i,j;
	// setIO("input");
	scanf("%d%d%d",&n,&m,&k);
	for(i=1;i<=m;++i) scanf("%d%d%d",&e[i].u,&e[i].v,&e[i].c);
	for(i=1;i<=n;++i) p[i]=i;
	sort(e+1,e+1+m,cmp);
    tot=n;
	for(i=1;i<=m;++i) {
		int u=e[i].u,v=e[i].v,c=e[i].c;
		int x=find(u),y=find(v);
		if(x!=y) {
			++tot;
			p[tot]=tot;
			maxv[tot]=c;
			p[x]=p[y]=tot;
			tree::addedge(tot,x),tree::addedge(tot,y);
		}
	}
	tree::dfs1(tot,0);
	tree::dfs2(tot,tot);
	for(i=1;i<=k;++i) {
		int x,y;
		scanf("%d%d",&x,&y);
		printf("%d\n",maxv[tree::LCA(x,y)]);
	}
	return 0;
}