Luogu P3366 【模板】最小生成树

qwq

$kruskal$算法

按边权从小到大排序，并查集合并即可。

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

int fa[200005];
int n,m;

struct abc {
    int from,to,w;
} q[200005];

int getfa(int x) {
    if(fa[x] == x)return fa[x];
    else return fa[x] = getfa(fa[x]);
}

bool cmp(abc x,abc y) {
    return x.w < y.w;
}

int kruskal() {
    int ans = 0;
    for(int i = 1; i <= n; i++) {
        fa[i] = i;
    }
    sort(q+1,q+m+1,cmp);
    for(int i = 1; i <= m; i++) {
        int l = getfa(q[i].from);
        int r = getfa(q[i].to);
        if(l != r) {
            fa[l] = r;
            ans += q[i].w;
        }
    }
    return ans;
}

int main() {
    scanf("%d%d",&n,&m);
    for(int i = 1; i <= m; i++) {
        scanf("%d%d%d",&q[i].from,&q[i].to,&q[i].w);
    }
    printf("%d",kruskal());
    return 0;
}