codeforces Educational Codeforces Round 78 (Rated for Div. 2) C - Berry Jam（折半枚举）

#include<bits/stdc++.h>
using namespace std;
const int maxn=2e5+1;
map<int,int>p;
int main()
{
	int n,T,ans,sum[2*maxn],t;
	scanf("%d",&T);
	while(T--)
	{
		scanf("%d",&n);
		p.clear();
		for(int i=0;i<=n;++i) sum[i]=0;
		p[0]=0;
		for(int i=1;i<=2*n;++i)
		{
			scanf("%d",&t);
			if(t==1) sum[i]=sum[i-1]+1;
			else sum[i]=sum[i-1]-1;
			if(i<=n) p[sum[i]]=i;//差值有可能是负的，所以要用map 
		}
		ans=2*n;
		for(int i=n;i<=2*n;++i)
		{
			int t1=sum[i]-sum[2*n];//相反数
			auto it=p.find(t1);
			if(it!=p.end())  ans=min(ans,i-it->second);
		 } 
		 printf("%d\n",ans);
	}
}