HDU6035 2017多校第一场1003 树形DP

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参考：Bahuia的博客

重点在于理清子树的层次关系，对于单个点进行逐子树更新时的转移

#pragma comment(linker, "/STACK:1024000000,1024000000") #include<bits/stdc++.h>#include<stdio.h>#include<algorithm>#include<queue>#include<string.h>#include<iostream>#include<math.h>#include<set>#include<map>#include<vector>#include<iomanip>using namespace std;#define ll long long#define pb push_back#define FOR(a) for(int i=1;i<=a;i++)const int maxn=2e5+7;int vis[maxn];int color[maxn];int siz[maxn];ll sum[maxn];//遍历到当前位置,颜色为x的最高一批节点为根的子树大小vector<int>G[maxn];ll ans;ll dfs(int u,int fa){siz[u]=1;ll allson=0;int sz=G[u].size();for(int i=0;i<sz;i++){int v=G[u][i];if(v==fa)continue;ll pre=sum[color[u]];//递归前的sum值siz[u]+=dfs(v,u);ll add=sum[color[u]]-pre;//新链上的块大小ans+=(siz[v]-add)*(siz[v]-add-1)/2;allson+=siz[v]-add;//记录儿子节点v组成的连通块大小}sum[color[u]]+=allson+1;return siz[u];}int main(){int n,kase=0;while(~scanf("%d",&n)){memset(vis,0,sizeof vis);memset(sum,0,sizeof sum);int cnt=0;for(int i=1;i<=n;i++){scanf("%d",&color[i]);if(!vis[color[i]])cnt++;vis[color[i]]=1;G[i].clear();}for(int i=1;i<n;i++){int u,v;scanf("%d%d",&u,&v);G[u].pb(v);G[v].pb(u);}printf("Case #%d: ",++kase);if(cnt==1){printf("%lld\n",1ll*n*(n-1)/2);continue;}ans=0;dfs(1,-1);for(int i=1;i<=n;i++){if(!vis[i])continue;ans+=(n-sum[i])*(n-sum[i]-1ll)/2ll;}printf("%lld\n",1ll*n*(n-1)/2ll*cnt-ans);}}

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