HDU7339

果然要自己写一遍！！！

#include <bits/stdc++.h>
/*
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/hash_policy.hpp>
*/
using namespace std;

const double eps = 1e-10;
const double pi = 3.1415926535897932384626433832795;
const double eln = 2.718281828459045235360287471352;

#define f(i, a, b) for (int i = a; i <= b; i++)
#define scan(x) scanf("%d", &x)
#define mp make_pair
#define pb push_back
#define lowbit(x) (x&(-x))

#define fi first
#define se second
#define SZ(x) int((x).size())
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define summ(a) (accumulate(all(a), 0ll))

typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef vector<int> vi;

using ll=long long;

//HDU 7339
const ll qz[]={998244353,1000000007,-998244353-1000000007};
ll n,a[(int)1e5+9],sz[(int)1e5+9],son[(int)1e5+9],dfn[(int)1e5+9],revdfn[(int)1e5+9],dfncnt,ans;
ll val[(int)1e5+9];
vector<int> g[(int)1e5+9];

void dfs(int u,int fa){
    val[u]=val[fa]+a[u];
    sz[u]=1,dfn[u]=++dfncnt,revdfn[dfncnt]=u;
    for(auto it:g[u])if(it!=fa){
        dfs(it,u);
        son[u]=sz[it]>sz[son[u]]?it:son[u],sz[u]+=sz[it];
    }
}

map<ll,int> cn;

void dsu(int u,int fa){
    for(auto it:g[u])if(it!=fa&&it!=son[u]){
        dsu(it,u);
        cn.clear();
    }
    if(son[u])dsu(son[u],u);

    auto cal=[&](int now,int lca,int lcafa){
        ll need=val[now]-val[lca]-val[lcafa];
        return cn[-need];
    };

    for(auto it:g[u])if(it!=fa&&it!=son[u]){
        for(int i=dfn[it];i<dfn[it]+sz[it];++i){
            ans+=cal(revdfn[i],u,fa);
        }
        for(int i=dfn[it];i<dfn[it]+sz[it];++i)cn[val[revdfn[i]]]+=1;
    }
    ans+=cal(u,u,fa);
    cn[val[u]]+=1;
}

int main()
{
    scanf("%lld",&n);
    for(int i=1;i<=n;++i){
        char c;
        scanf(" %c",&c);
        a[i]=qz[c-'a'];
    }
    for(int i=1,x,y;i<n;++i){
        scanf("%d%d",&x,&y);
        g[x].push_back(y),g[y].push_back(x);
    }
    dfs(1,0);
    dsu(1,0);
    printf("%lld\n", ans);
    return 0;
}