P4769 [NOI2018]冒泡排序（dp）

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日常膜拜shadowice巨巨的题解

//minamoto
#include<bits/stdc++.h>
#define R register
#define ll long long
#define fp(i,a,b) for(R int i=a,I=b+1;i<I;++i)
#define fd(i,a,b) for(R int i=a,I=b-1;i>I;--i)
#define go(u) for(int i=head[u],v=e[i].v;i;i=e[i].nx,v=e[i].v)
template<class T>inline bool cmax(T&a,const T&b){return a<b?a=b,1:0;}
inline int min(const R int &x,const R int &y){return x<y?x:y;}
using namespace std;
char buf[1<<21],*p1=buf,*p2=buf;
inline char getc(){return p1==p2&&(p2=(p1=buf)+fread(buf,1,1<<21,stdin),p1==p2)?EOF:*p1++;}
int read(){
    R int res,f=1;R char ch;
    while((ch=getc())>'9'||ch<'0')(ch=='-')&&(f=-1);
    for(res=ch-'0';(ch=getc())>='0'&&ch<='9';res=res*10+ch-'0');
    return res*f;
}
const int N=6e5+5,P=998244353;
inline int add(R int x,R int y){return x+y>=P?x+y-P:x+y;}
inline int dec(R int x,R int y){return x-y<0?x-y+P:x-y;}
inline int mul(R int x,R int y){return 1ll*x*y-1ll*x*y/P*P;}
int ksm(R int x,R int y){
	R int res=1;
	for(;y;y>>=1,x=mul(x,x))if(y&1)res=mul(res,x);
	return res;
}
int fac[N<<1],inv[N<<1],mn[N],a[N];
int n;
inline int C(R int n,R int m){return m<0?0:mul(fac[n],mul(inv[m],inv[n-m]));}
inline int S(R int n,R int m){return m>n?0:dec(C((n<<1)-m,n-m),C((n<<1)-m,n-m-1));}
struct BI{
	int c[N];
	inline void upd(R int x,R int y){for(;x<=n;x+=x&-x)c[x]+=y;}
	inline int query(R int x){R int res=0;for(;x;x-=x&-x)res+=c[x];return res;}
	inline void clr(){fp(i,1,n)c[i]=0;}
}bi;
int main(){
//	freopen("testdata.in","r",stdin);
	fac[0]=inv[0]=1;fp(i,1,(N<<1)-5)fac[i]=mul(fac[i-1],i);
	inv[(N<<1)-5]=ksm(fac[(N<<1)-5],P-2);fd(i,(N<<1)-6,1)inv[i]=mul(inv[i+1],i+1);
	int T=read();
	while(T--){
		n=read();fp(i,1,n)a[i]=read();
		fp(i,1,n)bi.upd(a[i],1);
		mn[n]=a[n];fd(i,n-1,1)mn[i]=min(mn[i+1],a[i]);
		int mx=0,cmx=0,ans=0;
		fp(i,1,n){
			if(cmx>mn[i])break;ans=add(ans,S(n-i+1,bi.query(max(mx,a[i]))+1));
			if(a[i]<mx)cmax(cmx,a[i]);cmax(mx,a[i]),bi.upd(a[i],-1);
		}printf("%d
",ans);
		bi.clr();
	}return 0;
}