poj 1442 Treap实现名次树

Treap的入门题目，每个结点多维护一个size表示以它为根的子树的结点数，然后查kth的时候一层一层向下即可。

#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <ctime>
using namespace std;

struct Node 
{
    Node * ch[2];
    int r;      
    int v;      
    int s;
    int cmp( int x )
    {
        if ( x == v ) return -1;
        return x < v ? 0 : 1;
    }    
    void maintain()
    {
        s = 1;
        if ( ch[0] != NULL ) s += ch[0]->s;
        if ( ch[1] != NULL ) s += ch[1]->s;
    }
};

void rotate( Node * & o, int d )
{
    Node * k = o->ch[d ^ 1];
    o->ch[d ^ 1] = k->ch[d];
    k->ch[d] = o;
    o->maintain();
    k->maintain();
    o = k;
}

void insert( Node * & o, int x )
{
    if ( o == NULL )
    {
        o = new Node();
        o->ch[0] = o->ch[1] = NULL;
        o->v = x;
        o->r = rand();
        o->s = 1;
    }
    else
    {
        int d = ( x < o->v ? 0 : 1 );  
        insert( o->ch[d], x );
        if ( o->ch[d]->r > o->r )
        {
            rotate( o, d ^ 1 );
        }
        o->maintain();
    }
}

int kth( Node * o, int k )
{
    int tmp = ( o->ch[0] == NULL ? 0 : o->ch[0]->s );
    if ( k == tmp + 1 ) return o->v;
    else if ( k < tmp + 1 ) return kth( o->ch[0], k );
    else return kth( o->ch[1], k - tmp - 1 );
}

const int N = 30001;
int a[N];

int main ()
{
    int n, m;
    while ( scanf("%d%d", &n, &m) != EOF )
    {
        Node * root = NULL;
        for ( int i = 1; i <= n; i++ )
        {
            scanf("%d", a + i);
        }
        int tt, cnt = 1;
        for ( int i = 1; i <= m; i++ )
        {
            scanf("%d", &tt);
            while ( cnt <= tt )
            {
                insert( root, a[cnt++] );
            }
            printf("%d\n", kth( root, i ));
        }
    }
    return 0;
}