求解答疑惑，玄关

#include <bits/stdc++.h>
using namespace std;
int l[200010],r[200010],sum1,sum0,ans,n;
int main()
{
    cin>>n;
    for (int i=1;i<=n;i++){
        int x; cin>>x;
        sum1+=(x==1), sum0+=(x==0);
        int t=sum0-sum1+n;
        if (!l[t]&&t!=n/*在这*/) l[t]=i; 
        else r[t]=i;
    }
    for (int i=0;i<=2*n;i++) ans=max(ans,r[i]-l[i]);
    cout<<ans<<endl;
    return 0;
}