思路：树hash，先找树重心，重心最多两个，然后从以重心为根求出树的hash值，放进map里。

代码：

#pragma GCC optimize(2)#pragma GCC optimize(3)#pragma GCC optimize(4)#include
    
     using namespace std;#define y1 y11#define fi first#define se second#define pi acos(-1.0)#define LL long long//#define mp make_pair#define pb push_back#define ls rt<<1, l, m#define rs rt<<1|1, m+1, r#define ULL unsigned LL#define pll pair
     
      #define pli pair
      
       #define pii pair
       
        #define piii pair
        
         #define pdd pair
         
          #define mem(a, b) memset(a, b, sizeof(a))#define debug(x) cerr << #x << " = " << x << "\n";#define fio ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);//head const ULL B = 133;int n, m, f, sz[55], hz;vector
          
            g[55], rt;unordered_map
           
             mp0;map
            
             
              , int> mp1;void get_h(int u, int o) { sz[u] = 1; int mx = 0; for (int v : g[u]) { if(v != o){ get_h(v, u); sz[u] += sz[v]; mx = max(mx, sz[v]); } } mx = max(mx, n-sz[u]); if(mx < hz) vector
              
               ().swap(rt), rt.pb(u), hz = mx; else if(mx == hz) rt.pb(u);}ULL dfs(int u, int o) { sz[u] = 1; vector
               
                 vc; for (int v : g[u]) { if(v != o) { vc.pb(dfs(v, u)); sz[u] += sz[v]; } } if(vc.size() == 0) return 1; sort(vc.begin(), vc.end()); ULL t = 1, sum = 0; for (ULL x:vc) { sum += t*x; t *= B; } return sum*sz[u];}int main() { scanf("%d", &m); for (int cs = 1; cs <= m; ++cs) { scanf("%d", &n); int r; for (int i = 1; i <= n; ++i) { scanf("%d", &f); if(!f) r = i; else g[f].pb(i), g[i].pb(f); } hz = n; get_h(r, r); assert(rt.size() <= 2); assert(rt.size() >= 1); if(rt.size() == 2) { ULL a = dfs(rt[0], rt[0]); ULL b = dfs(rt[1], rt[1]); if(a > b) swap(a, b); if(mp1.find({a, b}) != mp1.end()) printf("%d\n", mp1[{a, b}]); else mp1[{a, b}] = cs, printf("%d\n", cs); } else { ULL a = dfs(rt[0], rt[0]); if(mp0.find(a) != mp0.end()) printf("%d\n", mp0[a]); else mp0[a] = cs, printf("%d\n", cs); } vector
                
                 ().swap(rt); for (int i = 1; i <= n; ++i) vector
                 
                  ().swap(g[i]); } return 0;}