郁闷的出纳员

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
const int N = 1e5 + 10, INF = 1e9;
int n, m, delta;
struct Node
{
    int s[2], p, v, size;
    void init(int _v, int _p)
    {
        v = _v, p = _p;
        size = 1;
    }
}tr[N];
int root, idx;

void pushup(int x)
{
    tr[x].size = tr[tr[x].s[0]].size + tr[tr[x].s[1]].size + 1;
}

void rotate(int x)
{
    int y = tr[x].p, z = tr[y].p;
    int k = tr[y].s[1] == x;
    tr[z].s[tr[z].s[1] == y] = x, tr[x].p = z;
    tr[y].s[k] = tr[x].s[k ^ 1], tr[tr[x].s[k ^ 1]].p = y;
    tr[x].s[k ^ 1] = y, tr[y].p = x;
    pushup(y), pushup(x);
}

void splay(int x, int k)
{
    while(tr[x].p != k)
    {
        int y = tr[x].p, z = tr[y].p;
        if(z != k){
            if((tr[y].s[1] == x) ^ (tr[z].s[1] == y)) rotate(x);
            else rotate(y);
        }
        rotate(x);
    }
    if(!k) root = x;
}

int insert(int v)
{
    int u = root, p = 0;
    while(u) p = u, u = tr[u].s[v > tr[u].v];
    u = ++ idx;
    if(p) tr[p].s[v > tr[p].v] = u;
    tr[u].init(v, p);
    splay(u, 0);
    return u;
}

int get(int v)
{
    int u = root, res;
    while(u)
    {
        if(tr[u].v >= v) res = u, u = tr[u].s[0];
        else u = tr[u].s[1];
    }
    return res;
}

int get_k(int k)
{
    int u = root;
    while(u)
    {
        if(tr[tr[u].s[0]].size >= k) u = tr[u].s[0];
        else if(tr[tr[u].s[0]].size + 1 == k) return tr[u].v;
        else k -= tr[tr[u].s[0]].size + 1, u = tr[u].s[1];
    }
    return -1;
}

int main()
{
    cin >> n >> m;
    int L = insert(-INF), R = insert(INF);
    
    int tot = 0;
    while(n --)
    {
        char op[2];
        int k;
        cin >> op >> k;
        if(*op == 'I')
        {
            if(k >= m) k -= delta, insert(k), tot ++;
        }
        else if(*op == 'A') delta += k;
        else if(*op == 'S')
        {
            delta -= k;
            R = get(m - delta);
            splay(R, 0), splay(L, R);
            tr[L].s[1] = 0;
            pushup(L), pushup(R);
        }
        else
        {
            if(tr[root].size - 2 < k) puts("-1");
            else cout << get_k(tr[root].size - k) + delta << endl;
        }
    }
    cout << tot - (tr[root].size - 2) << endl;
}