主席树模板

5.3解锁新姿势
弱弱也会主席树啦

题目：查找区间第K小

#include<iostream>
#include<vector>
#include<algorithm>
#include<cstring>
using namespace std;

const int N=100010;

struct Node{
int l,r;
int cnt;
}tr[N*4+N*17];

vector <int> num;
int a[N],idx,root[N];

int finx(int x)
{
    return lower_bound(num.begin(),num.end(),x)-num.begin();
}

int intree(int p,int l,int r,int x)
{
    int q=++idx;
    tr[q]=tr[p];
    if(l==r)
    {
        tr[q].cnt++;
        return q;
    }
    int mid=l+r>>1;
    if(x<=mid) tr[q].l=intree(tr[p].l,l,mid,x);
    else tr[q].r=intree(tr[p].r,mid+1,r,x);
    tr[q].cnt=tr[tr[q].l].cnt+tr[tr[q].r].cnt;
    return q;
}

int build(int l,int r)
{
    int p=++idx;
    if(l==r) return p;
    int mid=l+r>>1;
    tr[p].l=build(l,mid);
    tr[p].r=build(mid+1,r);
    return p;
}

int quary(int p,int q,int l,int r,int k)
{
    if(l==r) return l;
    int cnt=tr[tr[q].l].cnt-tr[tr[p].l].cnt;
    int mid=l+r>>1;
    if(cnt>=k) return quary(tr[p].l,tr[q].l,l,mid,k);
    else return quary(tr[p].r,tr[q].r,mid+1,r,k-cnt);
}

int main()
{
    int n,m;
    cin>>n>>m;
    for(int i=1;i<=n;i++)
    {
        scanf("%d",a+i);
        num.push_back(a[i]);
    }
    sort(num.begin(),num.end());
    num.erase(unique(num.begin(),num.end()),num.end());
    root[0]=build(0,num.size()-1);
    for(int i=1;i<=n;i++)
        root[i]=intree(root[i-1],0,num.size()-1,finx(a[i]));
    while(m--)
    {
        int l,r,k;
        scanf("%d%d%d",&l,&r,&k);
        printf("%d\n",num[quary(root[l-1],root[r],0,num.size()-1,k)]);
    }
}

标签：cnt,return,int,tr,mid,num,模板,主席
来源： https://blog.csdn.net/Hello_wcrd/article/details/116379869