9 July
并查集
int fa[];
for (int i=1; i<=n; ++i) fa[i]=i;
int f(int x){return fa[x]==x?x:fa[x]=f(fa[x]);}
void join(int x,int y) {x=f(x),y=f(y); f[x]=y;}
最小生成树
边从小到大添加，共 (n-1) 条。统计边权和。
P1195 口袋的天空:
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <queue>
using namespace std;
int n, m, K, cnt, fa[1003], sum;
struct node{int x,y,w;
bool operator <(const node&a)const{return w>a.w;}
};
priority_queue<node> G;
int fi(int x) {return fa[x]==x?x:fa[x]=fi(fa[x]); }
void join(int x,int y){fa[fi(x)]=fi(y);}
int main() {
scanf("%d%d%d", &n, &m, &K);
while (m--) {
int a,b,c;scanf("%d%d%d", &a,&b,&c);
G.push((node){a,b,c});
}
for (int i=1; i<=n; ++i) fa[i]=i;cnt=n;
while (!G.empty()){
node a=G.top();G.pop();
if (fi(a.x)!=fi(a.y)) join(a.x,a.y),sum+=a.w,--cnt;
if (cnt==K)break;
}
if (cnt!=K) printf("No Answer
");
else printf("%d
", sum);
return 0;
}