POJ 1679 The Unique MST 生成树

http://bailian.openjudge.cn/practice/1679

题解：次小生成树。

代码：

#include <iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;

const int maxn = 105;
const int maxm= 10005;
int p[maxn];
int finde(int x){
	if(p[x]==x)return x;
	return p[x]=finde(p[x]);
}
bool issame(int x,int y){
	x=finde(x);
	y=finde(y);
	return x==y;
}
void join(int x,int y){
	x=finde(x);
	y=finde(y);
	p[x]=y;
}
struct node{
	int a,b,w;
	bool select;
}e[maxm];
bool cmp(node a,node b){
	return a.w<b.w;
}
struct node1{
	int to,next;
};
node1 link[maxn];
int il;
int head[maxn];
int iend[maxn];
int length[maxn][maxn];
int n,m;
void kruskal(){
	int k=0;
	int i,x,y;
	int w,v;
	for(il=0;il<=n;il++){
		link[il].to=il+1;
		link[il].next=head[il+1];
		iend[il+1]=il;
		head[il+1]=il;
	}
	sort(e,e+m,cmp);
	for(i=0;i<m;i++){
		if(k==n-1)break;
		if(e[i].w<0)continue;
		x=finde(e[i].a);
		y=finde(e[i].b);
		if(x!=y){
			for(w=head[x];w!=-1;w=link[w].next){
				for(v=head[y];v!=-1;v=link[v].next){
					length[link[w].to][link[v].to]=length[link[v].to][link[w].to]=e[i].w;
				}
			}
			link[iend[y]].next=head[x];
			iend[y]=iend[x];
			join(x,y);
			k++;
			e[i].select=true;
		}
	}
	return ;
}
void init(){
	int i;
	for(i=1;i<=n;i++)p[i]=i;
	memset(head,-1,sizeof(head));
	memset(length,0,sizeof(length));
	//memset(e,0,sizeof(e));
}
int main()
{
	int t,i;
	scanf("%d",&t);
	while(t--){
		scanf("%d%d",&n,&m);
		init();
		for(i=0;i<m;i++){scanf("%d%d%d",&e[i].a,&e[i].b,&e[i].w);e[i].select=false;}
		kruskal();
		int mst=0;
		for(i=0;i<m;i++)if(e[i].select)mst+=e[i].w;
		int secmst=0x3f3f3f3f;
		for(i=0;i<m;i++){
			if(!e[i].select){
				secmst=min(secmst,mst+e[i].w-length[e[i].a][e[i].b]);
			}
		}
		if(mst!=secmst)printf("%d\n",mst);
		else printf("Not Unique!\n");
	}
    //cout << "Hello world!" << endl;
    return 0;
}