fisher-yates

Example:

例：

Say the input array is [1, 2 3, 4, 5 6, 7]After reshuffling it can be anything like [4, 3, 7, 2, 1, 5, 1]

Our goal is that the reshuffling should be as random as possible.

我們的目標(biāo)是，改組應(yīng)盡可能地隨機(jī)。

There is a standard algorithm named Fisher-Yates algorithm which shuffles the array in linear times.

有一個(gè)名為Fisher-Yates算法的標(biāo)準(zhǔn)算法，可以在線性時(shí)間內(nèi)對(duì)數(shù)組進(jìn)行隨機(jī)排序。

The idea is to start from an end

這個(gè)想法是從頭開始

Say we are string from the right end and the array size is n

假設(shè)我們是從右端開始的字符串，數(shù)組大小為n

Now, pick the end element which will be the nth element, and pick up another element randomly from the range [0, n-1]. Then swap the elements and shrink the right end. Thus after this step, a[n-1](the rightmost element) is fixed. Continue the same until we reach the left end.

現(xiàn)在，選擇將成為第n個(gè)元素的end元素，并從[0，n-1]范圍內(nèi)隨機(jī)選擇另一個(gè)元素。 然后交換元素并縮小右端。 因此，在此步驟之后， a [n-1] (最右邊的元素)被固定。 繼續(xù)同樣操作，直到到達(dá)左端。

The detailed algorithm will be,

詳細(xì)的算法將是

For i=n-1 to 1Pick and element in the range [0,i-1] randomlySwap the randomly picked element with a[i]Decrement i End for loop

Since, it's random we can't do dry run

因?yàn)檫@是隨機(jī)的，所以我們不能空運(yùn)行

But still to illustrate lets pick elements randomly as per thought

但仍需說明讓我們根據(jù)想法隨機(jī)選擇元素

So initially, Array is[1, 2 3, 4, 5 6, 7]So i=6Say, we picked up 4^th (0-indexed) element randomly (in the range [0-5])Swap them So array is now [1, 2, 3, 4, 7, 6, 5]So 5 is now fixed and is guaranteed to stay there after the whole shuffling completes On the next iteration i will be 5 and we will continue similar way until I becomes 1

C++ implementation:

C ++實(shí)現(xiàn)：

#include <bits/stdc++.h> using namespace std;//reference to array is passed as we need //to update the array within the functionvoid reshuffle(vector<int>& arr, int n) {srand(time(0));for (int i = n - 1; i >= 1; i--) {//j will be a random no with in range 0 to i-1int j = rand() % i;//swap ith index with jthint temp = arr[i];arr[i] = arr[j];arr[j] = temp;} }int main() {cout << "input array size\n";int n;cin >> n;cout << "Input array elements \n";vector<int> arr(n);for (int i = 0; i < n; i++) {cin >> arr[i];}reshuffle(arr, n);cout << "After reshuffling, printing the array\n";for (auto it : arr)cout << it << " ";cout << endl;return 0; }

Output:

輸出：

input array size 6 Input array elements 12 34 32 56 48 11 After reshuffling, printing the array 56 48 12 11 32 34

Real-life applications:

實(shí)際應(yīng)用：

Creating an application which will suggest movie/songs from a list randomly. But each time it would suggest a unique movie only.

創(chuàng)建一個(gè)可以從列表中隨機(jī)建議電影/歌曲的應(yīng)用程序。 但是每次都會(huì)只推薦一部獨(dú)特的電影。

In this case, what we will do is we will show the i^th indexed movie after each iteration. As the i^th indexed one is never going to come again in the reshuffling as that's being fixed every time. That means we will recommend ith song/movie after the swap is done at each stage.

在這種情況下，我們要做的是在每次迭代后顯示第i ^個(gè)索引的電影。 由于第i ^個(gè)被索引的索引永遠(yuǎn)不會(huì)在改組中再次出現(xiàn)，因?yàn)槊看味脊潭ā?這意味著在每個(gè)階段完成交換后，我們將推薦第i首歌曲/電影。

Go through the below link to understand the detailed problem and solution.

瀏覽以下鏈接以了解詳細(xì)的問題和解決方案。

翻譯自: https://www.includehelp.com/data-structure-tutorial/shuffle-a-given-array-in-o-n-time-using-fisher-yates-shuffle-algorithm.aspx

fisher-yates

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