2021.8.14提高B组模拟6T3 + P7527 [USACO21OPEN] United Cows of Farmer John （树状数组）

Posted 2022-01-10 SSL_LKJ

United Cows of Farmer John

题目传送门

解题思路

树状数组乱糊

AC代码

#include<cstdio>
#include<cstring>
using namespace std;
long long n,ans,a[200005],f[200005],t[200005];//答案要long long 
long long lowbit(long long x)//处理 

	return x&(-x);

void update(long long x,long long y)//修改 

	for(long long i=x;i<=n;i+=lowbit(i))t[i]+=y;

long long query(long long x)//查询 

	long long sum=0;
	for(long long i=x;i;i-=lowbit(i))sum+=t[i];
	return sum;

int main()

	scanf("%lld",&n);
	for(long long i=1;i<=n;i++)
	
		scanf("%lld",&a[i]);
		f[i]=n+1;//初值 
	
	for(long long i=n;i>=1;i--)//枚举起点 
	
		ans+=query(f[a[i]]-1);
		update(f[a[i]],-1);//修改区间的数的种类数 
		update(i,1);
		f[a[i]]=i;	//修改位置 
	
	printf("%lld",ans);
	return 0;

谢谢