【康復訓練】【主席樹】【51nod】1175 區間中第K大的數

Description

一個長度爲N的整數序列，編號0 - N - 1。進行Q次查詢，查詢編號i至j的所有數中，第K大的數是多少。
例如: 1 7 6 3 1。i = 1, j = 3，k = 2，對應的數爲7 6 3，第2大的數爲6。

題解

主席樹

代碼

#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxn 50006
#define maxs 1600006
using namespace std;
inline char nc(){
    static char buf[100000],*i=buf,*j=buf;
    return i==j&&(j=(i=buf)+fread(buf,1,100000,stdin),i==j)?EOF:*i++;
}
inline int _read(){
    char ch=nc();int sum=0;
    while(!(ch>='0'&&ch<='9'))ch=nc();
    while(ch>='0'&&ch<='9')sum=sum*10+ch-48,ch=nc();
    return sum;
}
struct node{
    node *l,*r;
    int L,R,s;
    node(int x=0,int y=0){L=x;R=y;s=0;}
}nil,base[maxs];
typedef node* p_node;
p_node null=&nil,len=base,rot[maxn];
int n,m,T,a[maxn],b[maxn];
p_node newnode(int l,int r){
    *len=node(l,r);len->l=len->r=null;
    return len++;
}
p_node build(int l,int r){
    p_node x=newnode(l,r);
    if(l>=r)return x;
    int mid=l+r>>1;
    x->l=build(l,mid);x->r=build(mid+1,r);
    return x;
}
p_node update(p_node lst,int k){
    p_node x=newnode(lst->L,lst->R);
    x->l=lst->l;x->r=lst->r;
    if(lst->L==lst->R)return x->s++,x;
    int mid=lst->L+lst->R>>1;
    if(k<=mid)x->l=update(x->l,k);
         else x->r=update(x->r,k);
    x->s=x->l->s+x->r->s;
    return x;
}
int query(p_node lst1,p_node lst2,int k){
    if(lst1->L==lst1->R)return b[lst1->L];
    int tem=lst2->r->s-lst1->r->s;
    if(k<=tem)return query(lst1->r,lst2->r,k);
         else return query(lst1->l,lst2->l,k-tem);
}
int main(){
    null->l=null->r=null;
    freopen("chairman.in","r",stdin);
    freopen("chairman.out","w",stdout);
    n=_read();
    for(int i=1;i<=n;i++)b[i]=a[i]=_read();
    sort(b+1,b+1+n);
    m=unique(b+1,b+1+n)-b-1;
    rot[0]=build(1,m);
    for(int i=1;i<=n;i++)rot[i]=update(rot[i-1],lower_bound(b+1,b+1+m,a[i])-b);
    T=_read();
    while(T--){
        int l=_read(),r=_read(),k=_read();
        printf("%d\n",query(rot[l],rot[r+1],k));
    }
    return 0;
}