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;}