P4769 [NOI2018]冒泡排序（dp）

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\n",ans);

		bi.clr();

	}return 0;

}
巴特西

P4769 [NOI2018]冒泡排序（dp）

最新文章

热门文章
