有没有大佬帮我看看这篇代码的复杂度

#include<bits/stdc++.h>
using namespace std;
char s[2000050];
long long dp[2000050],to[2000050];
long long ans=0;
int main()
{
	//freopen("game3.in","r",stdin);
	ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
	int n;
	cin>>n;
	cin>>s+1;
	for (int i=1;i<=n;i++)dp[i]=1;
	dp[0]=1;
	for (int i=1;i<n;i++)
	{
		if (!to[i]){
		stack<pair<char,int> >q;
		q.push(make_pair(s[i],i));
		int j; 
		for (j=i+1;j<=n;j++)
		{
			if (s[j]==q.top().first)
			{
				to[q.top().second]=j;
				q.pop();
			}
			else 
			{
				if (to[j])
				{
					j=to[j];
					continue;
				}
				q.push(make_pair(s[j],j));
			}
			if (q.empty())break;
		}
		}
		if (to[i])
		{
			dp[to[i]]+=dp[i-1];
			ans+=dp[i-1];
		}
	}
	cout<<ans;
	return 0;
}