这段一直卡在 $30$ 分，帮帮忙，感谢

#include<bits/stdc++.h>
using namespace std;
#define int long long
const int n = 2E5+10;
int N, num, sumt, ans, na, nu, L[n], R[n];
signed main(){
	scanf("%lld", &N); for(int i = 1; i <= N; ++ i){
		scanf("%lld", &num);
		if(num) ++ na;
		else ++ nu;
		sumt = nu - na + N;
		if(sumt not_eq n && not L[sumt]) L[sumt] = i;
		else R[sumt] = i;
	} for(int i = 0; i <= N * 2; ++ i){
		ans = max(ans, abs(R[i] - L[i]));
	} printf("%lld", ans);
	return 0;
}