bzoj3594 方伯伯的玉米田 树状数组优化dp

f[i][j]表示到第i位，使用了j次机会的最长不下降子序列长度

转移：f[i][j]=max(f[x][y])+1;

x<i; y<=j; a[x]+y<=a[i]+j;

所以根据后两个条件维护二维树状数组求最值

#include<cstdio>
#include<cstring>
#include<iostream>
using namespace std;
int n,m,k;
int a[10005],c[505][5505],f[10005][505];
int lowbit(int x){return x&(-x);}
int query(int x,int y){
    int ans=0;
    while(x){
        int i=y;
        while(i){
            ans=max(ans,c[x][i]);
            i-=lowbit(i);
        }
        x-=lowbit(x);
    }
    return ans;
}
void update(int x,int y,int z){
    while(x<=k+1){
        int i=y;
        while(i<=m){
            c[x][i]=max(c[x][i],z);
            i+=lowbit(i);
        }
        x+=lowbit(x);
    }
}
int main()
{
    //freopen("data.in","r",stdin);
    //freopen("data.out","w",stdout);
    scanf("%d%d",&n,&k);
    for(int i=1;i<=n;i++){
        scanf("%d",&a[i]);
        m=max(m,a[i]);
    }
    //printf("666\n");
    m+=k;  int ans=0;
    for(int i=1;i<=n;i++){
        for(int j=0;j<=k;j++){
            f[i][j]=query(j+1,a[i]+j)+1;
            ans=max(ans,f[i][j]);
        }
        for(int j=0;j<=k;j++)
            update(j+1,a[i]+j,f[i][j]);
    }
    printf("%d\n",ans);
    return 0;
}