L3-002 特殊堆栈

#include <bits/stdc++.h>

using namespace std;

const int N = 1E5 + 10;
int tr[N];
stack<int> stk;

int lowbit(int x) {
    return x & -x;
}

void add(int x, int d) {
    for (int i = x; i < N; i += lowbit(i)) {
        tr[i] += d;
    }
}

int query(int x) {
    int res = 0;
    for (int i = x; i; i -= lowbit(i)) {
        res += tr[i];
    }
    return res;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n;
    cin >> n;
    for (int i = 0; i < n; i++) {
        string op;
        cin >> op;
        if (op == "Pop") {
            //cout << op << " ";
            if (stk.empty()) {
                cout << "Invalid" << "\n";
            } else {
                int x = stk.top();
                stk.pop();
                cout << x << "\n";
                add(x, -1);
            }
        } else if (op == "PeekMedian") {
            //cout << "PeekMedian" << " ";
            if (stk.empty()) {
                cout << "Invalid" << "\n";
            } else {
                int md = ((int)stk.size() + 1) / 2;
                int l = 0, r = 100000;
                while (l < r) {
                    int mid = l + r >> 1;
                    if (query(mid) >= md) r = mid;
                    else l = mid + 1;
                }
                cout << l << "\n";
            }
        } else {
            //cout << "Push" << " ";
            int x;
            cin >> x;
            stk.push(x);
            add(x, 1);
        }
    } 

    return 0;
}