HDU3938 并查集 并查集

先按边权值排个序，每次加入一条边，用并查集，关键看懂题。

#include <cstdio>#include <cstring>#include <algorithm>#include <cmath>using namespace std;const int MAXN = 10010;int N,M,Q;struct Edge{int a,b;int cost;void input(){scanf("%d%d%d",&a,&b,&cost);a--;b--;}}edges[MAXN*5];inline int cmp(Edge a,Edge b){return a.cost < b.cost;}struct Qs{int index,t;}q[MAXN];int ans[MAXN];inline int cmp1(Qs a,Qs b){return a.t < b.t;}int f[MAXN],r[MAXN];inline int find(int x){    if(x != f[x]){    f[x] = find(f[x]);    }    return f[x];}int main(){while (scanf("%d%d%d",&N,&M,&Q) != EOF){for(int i = 0; i < M; ++i)edges[i].input();sort(edges,edges+M,cmp);for(int i = 0; i < Q; ++i){scanf("%d",&q[i].t);q[i].index = i;}sort(q,q+Q,cmp1);int st = 0,sum;for(int i = 0; i < N; ++i){r[i] = 1;f[i] = i;}sum = 0;for(int i = 0; i < Q; ++i){while (st < M && q[i].t >= edges[st].cost){if(find(edges[st].a) != find(edges[st].b)){int a = r[f[edges[st].a]],b = r[f[edges[st].b]];sum += (a+b)*(a+b-1)/2 - a*(a-1)/2 - b*(b-1)/2;r[f[edges[st].a]] = a+b;f[f[edges[st].b]] = f[edges[st].a];}st ++;}ans[q[i].index] = sum;}for(int i = 0; i < Q; ++i){printf("%d\n",ans[i]);}}return 0;}