st解君愁

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
ll T=1;const ll N=2e5+5;
ll n,x,y;ll cnt;ll pre[N];
void solve(){
	cin>>n;string a;cin>>a;

	ll l=1;ll r=2;a=" "+a;
	set<char>st;
	while(r<=n){
		if(st.find(a[r])==st.end()){
			st.insert(a[r]);
			cnt=max(cnt,r-l+1);r++;
		}else{
			st.erase(a[l]);l++;
		}
		
	}cout<<cnt;
}

int main(){
	while(T--)solve();
	return 0;
} 
```echarts