c ++明明的随机数

Problem statement:

问题陈述：

Write an application code that will suggest movies from a list randomly and there won't be any repeat while suggesting the movies. That means the same movie won't be suggested twice though it will be done randomly. Input will be a movie list.

编写应用程序代码，以随机建议列表中的电影，并且在建议电影时不会重复。 这意味着尽管会随机播放同一部电影，但不会两次被推荐。 输入将是电影列表。

Prerequisite:

先决条件：

Example:

例：

Input:["D-DAY", "RAINCOAT", "OCTOBER","LUNCHBOX", "BARFI", "RAAZI","PIKU"]Movie suggestion list can be"BARFI""PIKU""RAAZI""OCTOBER""D_DAY""LUNCHBOX""RAINCOAT"

Solution

解

We can use Fisher-Yates random shuffling algorithm to solve this problem. Firstly, we need to create a map to store indexes of the movies as we will shuffle based on their indexes.

我们可以使用Fisher-Yates随机改组算法来解决此问题。 首先，我们需要创建一个地图来存储电影的索引，因为我们将根据电影的索引进行随机播放。

So the map will be:

因此，地图将为：

KEY	VALUE1	"D-DAY"2	"RAINCOAT"3	"OCTOBER"4	"LUNCHBOX"5	"BARFI"6	"RAAZI"7	"PIKU"

So our movie list will be converted as: [1,2,3,4,5,6,7]

因此，我们的电影列表将被转换为：[1,2,3,4,5,6,7]

Then we will shuffle using the Fisher-Yates algorithm

然后，我们将使用Fisher-Yates算法进行洗牌

At each step iteration, we will suggest movie[i]. Below is the detailed algorithm for suggesting movie randomly

在每一步迭代中，我们都会建议movie [i] 。 以下是随机建议电影的详细算法

The detailed algorithm will be,

详细的算法将是

For i=n-1 to 1    Pick and element in the range [0,i-1] randomly    Swap the randomly picked element with a[i]    // since it's not going to be reshuffled again     // as we are decrementing i ,     // thus it's guaranteed that it won't be suggested twice     Recommend movie[a[i]]Decrement iEnd for loop

So, how this guarantees unique suggestion each time?

那么，如何保证每次的独特建议呢？

Because, we are fixing the i^th element after the swap and decrementing i, so that the movie that got suggested never takes part again in swaps.

因为，我们在交换之后固定了^第 i ^个元素，并减小了i ，以便所建议的电影再也不会参与交换。

C++ Implementation:

C ++实现：

#include 
    
     using namespace std;void recommend_movie_randomly(vector
     
       movies){    srand(time(0));    map
      
        mymap;    int n = movies.size();    for (int i = 0; i < n; i++) {        mymap[i] = movies[i];    }    vector
       
         arr(n); //stores the indexes    for (int i = 0; i < n; i++)        arr[i] = i;    //shiffling randomly and suggesting movie     //at each iteartion    for (int i = n - 1; i >= 1; i--) {        //j will be a random no with in range 0 to i-1        int j = rand() % i;        //swap ith index with jth        int temp = arr[i];        arr[i] = arr[j];        arr[j] = temp;        //suggest the ith movie now        cout << "Suggesting next movie...\n";        cout << mymap[arr[i]] << endl;    }}int main(){    //input list    vector
        
          movie_list{ "D-DAY", "RAINCOAT", "OCTOBER", "LUNCHBOX", "BARFI", "RAAZI", "PIKU" };    cout << "Recommending movies randomly from the list\n";    recommend_movie_randomly(movie_list);    return 0;}
        
       
      
     
    

Output:

输出：

Recommending movies randomly from the listSuggesting next movie...RAAZISuggesting next movie...OCTOBERSuggesting next movie...PIKUSuggesting next movie...D-DAYSuggesting next movie...RAINCOATSuggesting next movie...LUNCHBOX

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c ++明明的随机数