Andrew and Chemistry(树的同构)

Andrew and Chemistry(树的同构)

题链

将一棵树转化为最小表示法，将此时的树哈希一下，同时用map进行标记，就可以判断树是否存在同构

#include <map>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <iostream>
#define scan(x) scanf("%d",&x)
#define scan2(x,y) scanf("%d%d",&x,&y)
using namespace std;
const int Max=1e5+10;
vector<int> a[Max];
map<int,map<int,int> >vis;
map<vector<int>,int>mat;
bool book[Max*100];
int cnt=0;
int dfs(int u,int fa){
     if(vis[u][fa]) return vis[u][fa];
     vector<int> tmp;
     for(int i=0;i<a[u].size();i++)
        if(a[u][i]!=fa)
            tmp.push_back(dfs(a[u][i],u));
     sort(tmp.begin(),tmp.end());
     if(!mat[tmp]) mat[tmp]=++cnt;
     return vis[u][fa]=mat[tmp];
}
int main()
{
    int n,u,v,ans=0;
    scan(n);
    for(int i=1;i<n;i++){
        scan2(u,v);
        a[u].push_back(v);
        a[v].push_back(u);
    }
    for(int i=1;i<=n;i++){
        if(a[i].size()==4) continue;
        v=dfs(i,0);
        if(!book[v]) ans++;
        book[v]=true;
    }
    printf("%d\n",ans);
    return 0;
}