PAT--1129 Recommendation System

題目鏈接：https://pintia.cn/problem-sets/994805342720868352/problems/994805348471259136

題目大意：在用戶點擊第i個商品前，求出應該推薦的商品（最多k個）。

直接看代碼吧

#include <bits/stdc++.h>
using namespace std;
const int N = 5e4 + 5;
int n, k, shu[N];
struct node {
	int num, cnt;
	node(int num = 0, int cnt = 0) {
		this->num = num;
		this->cnt = cnt;
	}
	bool operator < (const node &a) const {
		return cnt != a.cnt ? cnt > a.cnt : num < a.num;
	}
};
set<node> s;
int main() {
	int x, count;
	scanf("%d %d", &n, &k);
	for(int i = 0; i < n; i++) {
		scanf("%d", &x);
		if(i) {
			printf("%d:", x);
			count = 0;
			set<node>::iterator it;
			for(it = s.begin(); it != s.end() && count < k; it++) {
				printf(" %d", it->num);
				count++;
			}
			printf("\n");
		}
		set<node>::iterator it = s.find(node(x, shu[x]));
		if(it != s.end()) s.erase(it);
		shu[x]++;
		s.insert(node(x, shu[x]));
	}
	return 0;
}