zoukankan      html  css  js  c++  java
  • 1129 Recommendation System

    1129 Recommendation System (25 分)

    Recommendation system predicts the preference that a user would give to an item. Now you are asked to program a very simple recommendation system that rates the user's preference by the number of times that an item has been accessed by this user.

    Input Specification:

    Each input file contains one test case. For each test case, the first line contains two positive integers: N (≤ 50,000), the total number of queries, and K (≤ 10), the maximum number of recommendations the system must show to the user. Then given in the second line are the indices of items that the user is accessing -- for the sake of simplicity, all the items are indexed from 1 to N. All the numbers in a line are separated by a space.

    Output Specification:

    For each case, process the queries one by one. Output the recommendations for each query in a line in the format:

    where query is the item that the user is accessing, and rec[i] (i=1, ... K) is the i-th item that the system recommends to the user. The first K items that have been accessed most frequently are supposed to be recommended in non-increasing order of their frequencies. If there is a tie, the items will be ordered by their indices in increasing order.

    Note: there is no output for the first item since it is impossible to give any recommendation at the time. It is guaranteed to have the output for at least one query.

    知识点:STL的使用,排序

    思路:每一次输入后,都要让所有元素有序。如果利用线性结构,那么他的时间复杂度是O(n),在数据量大的时候也是不行的。利用STL的set,插入的时间复杂度降为O(logN)

     1 #include <cstdio>
     2 #include <set>
     3 using namespace std;
     4 const int maxn = 500050;
     5 
     6 int clickTime[maxn];
     7 struct nodetype{
     8     int v,cnt;
     9     nodetype(int a,int b) : v(a), cnt(b) {}
    10     bool operator < (const nodetype &a) const    {
    11         return (cnt!=a.cnt)?cnt>a.cnt:v<a.v;
    12     }    
    13 };
    14 
    15 int main(int argc, char *argv[]) {
    16     fill(clickTime,clickTime+maxn,0);
    17     
    18     int n,k,tmp;
    19     scanf("%d %d",&n,&k);
    20     set<nodetype> s;
    21     for(int i=1;i<=n;i++){
    22         scanf("%d",&tmp);
    23         if(i!=1){
    24             printf("%d:",tmp);
    25             int cnt=0;
    26             for(auto it=s.begin();cnt<k&&it!=s.end();it++){
    27                 printf(" %d",it->v);
    28                 cnt++;
    29             }
    30             printf("
    ");
    31         }
    32         
    33         auto it = s.find(nodetype(tmp,clickTime[tmp]));
    34         if(it!=s.end()){
    35             s.erase(nodetype(tmp,clickTime[tmp]));
    36         }
    37         s.insert(nodetype(tmp,clickTime[tmp]+1));
    38         clickTime[tmp]++;
    39     }
    40 }
  • 相关阅读:
    Pausing Coyote HTTP/1.1 on http-8080
    网站后台管理中生成首页失败
    Eclipse快捷键集结
    电子商务网站推广10大方法
    Eclipse使用
    注册表中更换桌面背景
    网站卡死,照惯例运行.bat批量处理文件进行重启不起作用
    同时处理html+js+jquery+css的插件安装(Spket&Aptana插件安装)
    JQuery的插件
    Eclipse插件
  • 原文地址:https://www.cnblogs.com/lokwongho/p/9908526.html
Copyright © 2011-2022 走看看