kruskal 【MST】

const int MAXN = 110;//点
const int MAXM = 10000;//边

int f[MAXN];//并查集使用

struct Edge
{
    int u, v, w;
}edge[MAXN];

int tol;//边数 初始化 0

void addedge(int u,int v,int w)
{
    edge[tol].u = u;
    edge[tol].v = v;
    edge[tol++].w = w;
}

bool cmp(Edge a,Edge b)
{
    return a.w < b.w;
}

int find(int x)
{
    if (f[x] == -1)
        return x;
    else
        return f[x] = find(f[x]);
}

int kruskal(int n)
{
    memset(f,-1,sizeof(f));
    sort(edge, edge+tol, cmp);
    int cnt = 0;
    int ans = 0;
    for (int i = 0; i < tol; i++)
    {
        int u = edge[i].u;
        int v = edge[i].v;
        int w = edge[i].w;
        int t1 = find(u);
        int t2 = find(v);
        if (t1 != t2)
        {
            ans += w;
            f[t1] = t2;
            cnt++;
        }
        if (cnt == n - 1)
            break;
    }
    if (cnt < n - 1) return -1;//不连通
    else return ans;
}