BZOJ 1046 [HAOI2007]上升序列

Posted 2020-10-25 zzyer

题解：f[i]表示以i开头的最长上升子序列长度

贪心先选下标最小的符合要求的元素

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int maxn=10009;

int n,T;
int maxlen;
int a[maxn];
int b[maxn],nn;

int c[maxn];
int lowbit(int x){
	return x&(-x);
}
void Addp(int x,int val){
	while(x<=nn){
		c[x]=max(c[x],val);
		x+=lowbit(x);
	}
}
int Querymax(int x){
	int ret=0;
	while(x){
		ret=max(ret,c[x]);
		x-=lowbit(x);
	}
	return ret;
}

int f[maxn];
int main(){
	scanf("%d",&n);
	for(int i=1;i<=n;++i){
		scanf("%d",&a[i]);
		a[i]=b[i]=-a[i];
	}
	sort(b+1,b+1+n);
	nn=unique(b+1,b+1+n)-b-1;
	for(int i=1;i<=n;++i)a[i]=lower_bound(b+1,b+1+nn,a[i])-b;
	for(int i=n;i>=1;--i){
		f[i]=Querymax(a[i]-1)+1;
		maxlen=max(maxlen,f[i]);
		Addp(a[i],f[i]);
	}
	
	scanf("%d",&T);
	while(T--){
		int l;
		scanf("%d",&l);
		if(l>maxlen){
			printf("Impossible\n");
		}else{
			int now=-0x7fffffff;
			for(int i=1;i<=n;++i){
				if((-b[a[i]]>now)&&(f[i]>=l)){
					printf("%d",-b[a[i]]);
					if(l!=1)printf(" ");
					now=-b[a[i]];
					if(--l==0)break;
				}
			}
			if(T)printf("\n");
		}
	}
	return 0;
}