洛谷P3149题解分享

原题目
https://www.luogu.com.cn/problem/P3149
代码

#include<bits/stdc++.h>
#define int  long long 
#define ls rt<<1
#define rs rt<<1|1
using namespace std;
const int N = 4e5+24;
int  tree[N<<2],tag[N<<2];
int a[N],b[N];
//a：二分数组 
set<int>q;
int f[N],nxd[N];

inline int rd(int &x){
	char c= getchar();
	int f= 1;
	while(c>'9'||c<'0'){
		if(c=='-')
			f=-f;
		c = getchar();
	}
	x = 0;
	do{
		x=(x<<1)+(x<<3)+c-'0';
		c=getchar();
	}while(c<='9'&&c>='0');
	x*=f;
	return x;
}//基操快读

inline void Push_up(int rt){
	tree[rt] = tree[ls]+tree[rs];
	return ;
}

void Build(int rt,int l,int r){
	if(l==r){
		tree[rt] = nxd[l];
		return ;
	}
	int mid = (l+r)>>1;
	Build(ls,l,mid);
	Build(rs,mid+1,r);
	Push_up(rt);
	return ;
}


void Modify(int rt,int l,int r,int L,int R,int x){
	if(L<=l&&R>=r){
		tree[rt]+=x*(r-l+1);
		return ;
	}
	int mid = (l+r)>>1;
	if(L<=mid)
		Modify(ls,l,mid,L,R,x);
	if(R>mid)
		Modify(rs,mid+1,r,L,R,x);
	Push_up(rt);
	return;
}


int  Query(int rt,int l,int r,int L,int R){
if(L<=l&&R>=r)
		return tree[rt];
	int mid =(l+r)>>1;
	int  ret=0;
	if(L<=mid)
		ret+=Query(ls,l,mid,L,R);
	if(R>mid)
		ret+=Query(rs,mid+1,r,L,R);
	return ret;
}

inline int Bin(int x,int L,int R){
	int  l =L,r = R,mid;
	do{
		mid = (l+r)>>1;
		if( a[mid] >= x )
			r = mid;
		else
			l = mid+1;
	}while(l<r);
	return l;
}//找到排位 


signed main(){
	int n,m,op,l,r,x,ret,ins;
	int opt,key;
	rd(m);rd(opt);
	
	for(int i=1;i<=m;i++){
		rd(b[i]);
		q.insert(b[i]);
	}
	//输入 
	n = 0;
	for(set<int>::iterator it  = q.begin();it!=q.end();it++){
		a[++n] = *it;
	}
	//建树 
	int  ans  = 0;
	int  k  = 0;
	int  rec  = 0;
	//rec记录不比当前大的正序对 
	for(int i=1;i<=m;i++){
		k = Bin(b[i],1,n);
		rec=Query(1,1,n,1,k);//正序对 
		Modify(1,1,n,k,k,1);
		f[k]+=rec;
	}
	int  cnt;
	for(int i=1;i<=n;i++){
		k = i;
		f[k]+=f[k-1];//全部正序对  
		cnt = Query(1,1,n,1,k);
		nxd[k] = (int)cnt*(cnt-1)/2 - f[k];//求得逆序对 
	}
	//狗屎预处理
	int up=-1;
	cout<<nxd[n]<<endl;
	int  answer;
	while(opt--){
		rd(key);
		key = b[key];
		key = Bin(key,1,n);
		up=max(up,key);
		answer = nxd[n]-nxd[up];
		cout<<answer<<endl;
	} 
	
	return 0;
} 
/*
5 2
1 5 3 4 2
3
4
*/