luogu P6564 [POI2007] 堆积木KLO 树状数组+dp

#include<bits/stdc++.h>
using namespace std;
const int N=1e6+10;
int a[N];
int n;
int tr[N];
int f[N];
int ans;
int lowbit(int x)
{
    return x&-x;
}
void add(int x, int c)
{
    for (int i = x; i <= n; i += lowbit(i)) 
        tr[i] =max(c,tr[i]);
}
int query(int x)
{
    int res = 0;
    for (int i = x; i; i -= lowbit(i)) 
        res =max(res,tr[i]); 
    return res;
}
struct node
{
    int v;
    int id;
} e[N];
//f[i]=max(f[j])+1
//j<i
//v[j]<v[i]
//v[i]-v[j]<=i-j   j-v[j]<=i-v[i]
//也就是按 j-v[j]<=i-v[i] 排序的最长上升序列 
//用树状数组维护 
bool cmp(node a,node b)
{
    if(a.id-a.v!=b.id-b.v)
        return a.id-a.v<b.id-b.v;
    return a.id<b.id;
}
int main()
{
    cin>>n;
    for(int i=1; i<=n; i++)
    {
        cin>>e[i].v;
        e[i].id=i;
    }
    sort(e+1,e+1+n,cmp);
    for(int i=1; i<=n; i++)
    {
        if(e[i].id-e[i].v<0)
            continue;
        f[i]=query(e[i].v-1) + 1;
        add(e[i].v,f[i]);
        ans=max(ans,f[i]);
    }
    cout<<ans<<endl;
    return 0;
}