哈希做法，#11 #12 TLE 死循环，求住

#include <bits/stdc++.h>
#define int long long
#define ull unsigned long long
using namespace std;
const int base = 131;

int n, ans;
string s, now;
stack<int> st;
unordered_map<ull, int> mp;
set<ull> se;
ull get_hash(string s){
    ull has = 0;
    for (int i = 0; i < s.size(); i++){
        has = has * base + s[i];
    }

    return has;
}
signed main(){
    //freopen("P9753_11.in", "r", stdin);
    //freopen("P9753_11.out", "w", stdout);

    cin >> n >> s;
    mp[0]++;
    for (int i = 0; i < n; i++){
        if (!st.empty() && st.top() == s[i] - 'a' + 1){
            now.pop_back();
            //cout << now << endl;
            ull h = get_hash(now);
            mp[h]++;
            st.pop();
            se.insert(h);
        }else{
            st.push(s[i] - 'a' + 1);
            now += s[i];
            //cout << now << endl;
            ull h = get_hash(now);
            mp[h]++;
            se.insert(h);
        }
    }


    for (auto it = se.begin(); it != se.end(); it++){
        int k = mp[*it];
        //cout << *it << " " << k << endl;
        ans += (k * (k - 1)) / 2;
    }

    cout << ans;

    return 0;
}