Review: 9-13 July

Posted 2022-03-31 greyqz

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 nodeint x,y,w;
    bool operator <(const node&a)constreturn 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;