Review: 9-13 July

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\n");
	else printf("%d\n", sum);
	return 0;
}

13 July

Review

• 数论
• 数学