2815: [ZJOI2012]灾难

来源：互联网发布：spss17.0软件下载编辑：程序博客网时间：2024/05/27 10:44

bz没有题面，，就不贴了= =

实际上有一种叫支配树的东西可以构造出答案，这题是支配树中最简单的= =因为原图是个DAG

blog传送门。。。。。。。。

大概是首先求个拓扑序，由拓扑序建树，每个点在它所有食物中找LCA，然后把这个点放在LCA下就行了

#include<iostream>#include<cstring>#include<vector>#include<queue>#include<algorithm>#include<cmath>#include<cstdio>using namespace std;const int maxn = 1E5 + 10;int n,m,ans[maxn],du[maxn],L[maxn],fa[maxn][17];bool vis[maxn];vector <int> v[maxn],v2[maxn],G[maxn];queue <int> Q;void Dfs(int x){ans[x] = 1;for (int i = 0; i < G[x].size(); i++){int to = G[x][i];Dfs(to); ans[x] += ans[to];}}int LCA(int p,int q){if (L[p] < L[q]) swap(p,q);for (int j = 16; j >= 0; j--)if (L[p] - (1<<j) >= L[q])p = fa[p][j];if (p == q) return p;for (int j = 16; j >= 0; j--)if (fa[p][j] != fa[q][j])p = fa[p][j],q = fa[q][j];return fa[p][0];}void Add(int k,int F){fa[k][0] = F; L[k] = L[F] + 1; G[F].push_back(k);for (int i = 1; i < 16; i++)if (fa[k][i-1] == -1) return;else fa[k][i] = fa[fa[k][i-1]][i-1];}int main(){#ifdef DMCfreopen("DMC.txt","r",stdin);#endifcin >> n;for (int i = 1; i <= n; i++){int x; scanf("%d",&x);while (x){v[x].push_back(i);v2[i].push_back(x);++du[i]; scanf("%d",&x);}}memset(fa,-1,sizeof(fa)); L[0] = 1;for (int i = 1; i <= n; i++)if (!du[i]) Q.push(i);while (!Q.empty()){int k = Q.front(),lca = k; Q.pop();for (int i = 0; i < v2[k].size(); i++){int fd = v2[k][i];if (!i) lca = fd;lca = LCA(lca,fd);}for (int i = 0; i < v[k].size(); i++){int to = v[k][i]; --du[to];if (!du[to]) Q.push(to);}if (lca == k) Add(k,0); else Add(k,lca);}Dfs(0);for (int i = 1; i <= n; i++) printf("%d\n",--ans[i]);return 0;}

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