treap模板

// Rank Tree
// Rujia Liu
// 输入格式：
// m     操作有m个
// 1 x   插入元素x
// 2 x   删除元素x。如果成功，输入1，否则输出0
// 3 k   输出第k小元素。k=1为最小元素
// 4 x   输出值x的“名次”，即比x小的结点个数加1
#include<cstdlib>

struct Node {
    Node *ch[2]; // 左右子树
    int r; // 随机优先级
    int v; // 值
    int s; // 结点总数
    Node(int v = 0):v(v)
    {
        ch[0] = ch[1] = NULL;
        r = rand();
        s = 1;
    }
    int cmp(int x) const
    {
        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(x);
    else {
        int d = (x < o->v ? 0 : 1); // 不要用cmp函数，因为可能会有相同结点
        insert(o->ch[d], x);
        if(o->ch[d]->r > o->r)
            rotate(o, d^1);
    }
    o->maintain();
}

Node* find(Node* o, int x)
{
    if(o == NULL)
        return NULL;
    if(x == o->v)
        return o;
    return x < o->v ? find(o->ch[0], x) : find(o->ch[1], x);
}

// 要确保结点存在
void remove(Node* &o, int x)
{
    int d = o->cmp(x);
    int ret = 0;//没什么用的样子
    if(d == -1) {
        Node* u = o;
        if(o->ch[0] != NULL && o->ch[1] != NULL) {
            int d2 = (o->ch[0]->r > o->ch[1]->r ? 1 : 0);
            rotate(o, d2);
            remove(o->ch[d2], x);
        } else {
            if(o->ch[0] == NULL)
                o = o->ch[1];
            else
                o = o->ch[0];
            delete u;//原版白书没有真实地将内存释放
        }
    } else
        remove(o->ch[d], x);
    if(o != NULL)
        o->maintain();
}

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

// 在以o为根的子树中，值比x小的结点总数加1
int rank(Node* o, int x)
{
    if(o == NULL)
        return 1;
    if(x <= o->v)
        return rank(o->ch[0], x);
    return rank(o->ch[1], x) + (o->ch[0] == NULL ? 0 : o->ch[0]->s) + 1;
}

#include<cstdio>
const int INF = 0x3f3f3f3f;

int main()
{
    int m,v;
    char c[5];
    Node* root = new Node(INF);
    while(scanf("%d", &m) == 1) {
        while(m--) {
            scanf("%s%d", &c, &v);
            if(c[0] == 'I')insert(root, v);
            else if(c[0] == 'C') printf("%d\n",rank(root, v));
            else if(c[0] == 'D') {
                Node* o = find(root, v);
                if(o != NULL)
                    remove(root, v);
            }else if(c[0] == 'K')
            if(v>root->s)puts("invalid");
            else printf("%d\n", kth(root, v));
        }
    }
    return 0;
}