题解 | 【模板】多重集合操作

#include<bits/stdc++.h>
using namespace std;

map<int, int> a;
int num;

void insertValue(int x) {
    //TODO 实现插入逻辑
    a[x]++;
    num++;
}
void eraseValue(int x) {
    //TODO 实现删除逻辑
    auto it = a.find(x);
    if (it == a.end()) return;
    it->second--;
    num--;
    if (it->second == 0) {
        a.erase(it);
    }
}
int xCount(int x) {
    //TODO 求x在集合中的个数
    auto it = a.find(x);
    return it->second;
}
int sizeOfSet() {
    //TODO 返回集合大小
    return num;
}
int getPre(int x) {
    //TODO 实现找前驱
    auto it = a.lower_bound(x);
    if (it != a.begin()) {
        --it;
        return it->first;
    }
    return -1;
}
int getBack(int x) {
    //TODO 实现找后继
    auto it = a.upper_bound(x);
    if (it != a.end()) {
        return it->first;
    }
    return -1;
}

int main() {
    int q, op, x;
    cin >> q;
    while (q--) {
        cin >> op;
        if (op == 1) {
            cin >> x;
            insertValue(x);
        }
        if (op == 2) {
            cin >> x;
            eraseValue(x);
        }
        if (op == 3) {
            cin >> x;
            cout << xCount(x) << endl;
        }
        if (op == 4) {
            cout << sizeOfSet() << endl;
        }
        if (op == 5) {
            cin >> x;
            cout << getPre(x) << endl;
        }
        if (op == 6) {
            cin >> x;
            cout << getBack(x) << endl;
        }
    }
    return 0;
}