code：

#include<bits/stdc++.h>
#define int long long
using namespace std;
signed main(){
    //freopen("game.in","r",stdin);
    //freopen("game.out","w",stdout);
    int n;
    cin>>n;
    string s;
    cin>>s;
    s='$'+s;
    int ans=0;
    stack<char>w;
    if(n<=10000){

        for(int i=1;i<=n;i++){
            while(w.size())w.pop();
            for(int j=i;j<=n;j++){
                if(w.size()==0||w.top()!=s[j])w.push(s[j]);
                else w.pop();
                if(w.size()==0)ans++;
            }
        }
        cout<<ans;
    }else{
        for(int i=1;i<=n;i++){
            while(w.size())w.pop();
            for(int j=i;j<=min(i+20,n);j++){
                if(w.size()==0||w.top()!=s[j])w.push(s[j]);
                else w.pop();
                if(w.size()==0)ans++;
            }
        }
        cout<<ans;

    }
    return 0;

}

洛谷上误交错无意间发现的。