题解 | 动态整数集最近值提取

#include <iostream>
#include <set>
#include <cmath>
using namespace std;

int main() {
    int q = 0;
    cin >> q;

    set<int> nums;
    for(int i = 0; i < q; i++) {
        int op,x;
        cin >> op >> x;

        if(op == 1) {
            if(nums.find(x) == nums.end()) {
                nums.insert(x);
                continue;
            } else {
                cout << "Already Exist" << endl;
                continue;
            }
        }
        if(op == 2) {
            if(nums.empty()) {
                cout << "Empty" << endl;
                continue;
            } else {

                if(nums.find(x) != nums.end()) {//判断x是否在set里，直接就省去了判断边界条件时相等的判断
                    cout << x << endl;
                    nums.erase(x);
                    continue;
                }
                int prev = -1;
                int last = -1;
                auto it = nums.lower_bound(x);// lower_bound是在set中找比x大于或等于的一个数的迭代器

                if(it == nums.begin()) { //查找set中的全部元素后，set的第一个元素就大于x
                    cout << *nums.begin() << endl;
                    nums.erase(*nums.begin());
                    continue;
                }
                if(it == nums.end()) { //查找set中的全部元素后，set中的(--end())也是小于x的，返回end()
                    cout << *(--nums.end()) << endl;
                    nums.erase(*(--nums.end()));
                    continue;
                }
                auto tmpit1 = it;
                auto tmpit2 = --it;
                // cout << "(tmpit2) " << *(tmpit2) << " (tmpit1) " << *(tmpit1) << endl;
                if(abs(*(tmpit2) - x) > abs(*(tmpit1) - x)) {
                    cout << *tmpit1 << endl;
                    nums.erase(*tmpit1);
                    continue;
                } else if (abs(*(tmpit2) - x) < abs(*(tmpit1) - x)) {
                    cout << *(tmpit2) << endl;
                    nums.erase(*(tmpit2));
                    continue;
                } else{
                    cout << *(tmpit2) << endl;
                    nums.erase(*(tmpit2));
                    continue;
                }
            }
        }

    }
}
// 64 位输出请用 printf("%lld")