文章标题 HDU 5977 : Garden of Eden （树分治）

参考自：http://blog.csdn.net/bahuia/article/details/53070036
代码：

#include <iostream>#include <cstdio>#include <cstring>#include <string>#include <queue>#include <set>#include <map>#include <algorithm>#include <math.h>#include <vector>using namespace std;typedef long long ll;const int inf = 0x3f3f3f3f;const int mod=1e9+7;const int maxn=5e4+10;int n,k,a[maxn];vector<int>sta;ll ha[1100],ans;struct Edge{    int to,nex;}edge[maxn*2];int tot,head[maxn],vis[maxn];void init(){    tot=0;    memset (head,-1,sizeof (head));    memset (vis,0,sizeof (vis));}void addedge(int u,int v){    edge[tot]=Edge{v,head[u]};    head[u]=tot++; }int sz[maxn],maxv[maxn],rt,Max,root;void dfs_size(int u,int pre){//求出每个子树的大小，以及每个节点的最大儿子     sz[u]=1;    maxv[u]=0;    for (int i=head[u];i!=-1;i=edge[i].nex){        int v=edge[i].to;        if (v==pre||vis[v])continue;        dfs_size(v,u);        sz[u]+=sz[v];        maxv[u]=max(maxv[u],sz[v]);    }}void dfs_root(int r,int u,int pre){//找出以u为根的子树的重心    maxv[u]=max(maxv[u],sz[r]-maxv[u]);    if (Max>maxv[u]){        Max=maxv[u];root=u;    }    for (int i=head[u];i!=-1;i=edge[i].nex){        int v=edge[i].to;        if (v==pre||vis[v])continue;        dfs_root(r,v,u);    }}void dfs_sta(int u,int fa,int s){    sta.push_back(s);    for (int i=head[u];i!=-1;i=edge[i].nex){        int v=edge[i].to;        if (v==fa||vis[v])continue;        dfs_sta(v,u,s|(1<<a[v]));    }}ll solve(int u,int s){//计算当前子树中合法的点对数    ll res=0;    sta.clear();    dfs_sta(u,-1,s);    memset (ha,0,sizeof (ha));    for (int i=0;i<sta.size();i++)ha[sta[i]]++;    for (int i=0;i<sta.size();i++){        ha[sta[i]]--;        res+=ha[(1<<k)-1];        for (int s0=sta[i];s0;s0=(s0-1)&sta[i]){            res+=ha[((1<<k)-1)^s0];         }        ha[sta[i]]++;    }    return res;} void dfs(int u,int num){//总的dfs求解    Max=n;    dfs_size(u,-1);    dfs_root(u,u,-1);    int rt=root;//一定要注意这样里的root是全局变量，在递归之后可能改变，需要提前保存下来。    vis[rt]=1;    ans+=solve(rt,1<<(a[rt]));    for (int i=head[rt];i!=-1;i=edge[i].nex){        int v=edge[i].to;        if (vis[v])continue;        ans-=solve(v,(1<<a[v])|(1<<a[rt]));    }    for (int i=head[rt];i!=-1;i=edge[i].nex){        int v=edge[i].to;        if (vis[v])continue;        dfs(v,sz[v]);    }}int main(){    while (scanf ("%d%d",&n,&k)!=EOF){        init();        for (int i=1;i<=n;i++){            scanf ("%d",&a[i]);            a[i]--;        }        int u,v;        for (int i=0;i<n-1;i++){            scanf ("%d%d",&u,&v);            addedge(u,v);            addedge(v,u);         }        if (k==1){            printf ("%lld\n",(ll)n*n);            continue;        }        ans=0;        dfs(1,n);        printf ("%lld\n",ans);    }    return 0;}/*3 21 2 21 21 3*/