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  • 最小生成树计数

    最小生成树计数

    #include <bits/stdc++.h>
    
    using namespace std;
    const int maxn=1010;
    const int mod=31011;
    struct edge{
        int u,v,w;
        bool operator<(const edge & b)const {
            return w<b.w;
        }
    }a[maxn];
    
    struct node{
        int l,r,num;
    }b[maxn];
    int  n,m,fa[maxn],num,tot,ans=1,sum;
    int fin(int x) {
        if (x == fa[x])
            return x;
        return fin(fa[x]);
    }
    
    void dfs(int i,int now,int k){
        if (now==b[i].r+1){
            if (k==b[i].num) sum++;
            return;
        }
        int u=fin(a[now].u),v=fin(a[now].v);
        if (u!=v){
            fa[u]=v;
            dfs(i,now+1,k+1);
            fa[u]=u;fa[v]=v;
        }
        dfs(i,now+1,k);
    }
    int main() {
        scanf("%d%d", &n, &m);
        for (int i = 1; i <= n; i++) fa[i] = i;
        for (int i = 1; i <= m; i++) {
            scanf("%d%d%d", &a[i].u, &a[i].v, &a[i].w);
        }
        sort(a + 1, a + m + 1);
        for (int i = 1; i <= m; i++) {
            if (a[i].w != a[i - 1].w) {
                b[++num].l = i;
                b[num - 1].r = i - 1;
            }
            int u = fin(a[i].u), v = fin(a[i].v);
            if (u != v) {
                fa[u] = v;
                tot++;
                b[num].num++;
            }
        }
        b[num].r = m;
        if (tot != n - 1) {
            printf("0
    ");
            return 0;
        }
        for (int i = 1; i <= n; i++) fa[i] = i;
        for (int i = 1; i <= num; i++) {
            sum = 0;
            dfs(i, b[i].l, 0);
            ans = ans * sum % mod;
            for (int j = b[i].l; j <= b[i].r; j++) {
                int u = fin(a[j].u), v = fin(a[j].v);
                if (u != v) fa[u] = v;
            }
        }
        printf("%d
    ", ans);
        return 0;
    }
    

      

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  • 原文地址:https://www.cnblogs.com/Accpted/p/11433240.html
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