4994: [Usaco2017 Feb]Why Did the Cow Cross the Road III

4994: [Usaco2017 Feb]Why Did the Cow Cross the Road III

Time Limit: 10 Sec  Memory Limit: 256 MB
Submit: 25  Solved: 20
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Description

给定长度为2N的序列，1~N各处现过2次，i第一次出现位置记为ai，第二次记为bi，求满足ai<aj<bi<bj的对数

Input

Output

Sample Input

4
3
2
4
4
1
3
2
1

Sample Output

3

刚开始写了个滑动窗口 写到一半发现GG

重新想一想 其实就是从前向后扫 每次询问区间内权值和

#include<cmath>#include<ctime>#include<cstdio>#include<cstring>#include<cstdlib>#include<iostream>#include<algorithm>#include<iomanip>#include<vector>#include<string>#include<bitset>#include<queue>#include<set>#include<map>using namespace std;typedef long long ll;inline int read(){int x=0,f=1;char ch=getchar();while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}while(ch>='0'&&ch<='9'){x=(x<<1)+(x<<3)+ch-'0';ch=getchar();}return x*f;}void print(ll x){if(x<0)x=-x,putchar('-');if(x>=10)print(x/10);putchar(x%10+'0');}const int N=100100;int n,w[N],s[N],bit[N];inline void modify(int x){for(;x<=n;x+=(x&-x))bit[x]++;}inline int query(int x){int res=0;for(;x;x-=(x&-x))res+=bit[x];return res;}bool book[N];int main(){n=read()<<1;register int i,x;for(i=1;i<=n;++i){x=read();if(!book[x])book[x]=1,w[x]=i;else s[w[x]]=i-w[x];}ll ans=0;modify(1+s[1]);for(i=2;i<=n;++i)if(s[i]){ans+=query(i+s[i])-query(i);modify(i+s[i]);}print(ans);puts("");return 0;}/*43 2 4 4 1 3 2 13*/