- Shuffling a list
Collections.shuffle() is used to shuffle lists in java.
Class hierarchy:
java
↳ util
↳ Collections
Syntax:
Collections.shuffle(list);
Examples:
Java
// Java program to demonstrate working of shuffle()import java.util.*;public class GFG { public static void main(String[] args) { ArrayList<String> mylist = new ArrayList<String>(); mylist.add("ide"); mylist.add("quiz"); mylist.add("neveropen"); mylist.add("quiz"); mylist.add("practice"); mylist.add("qa"); System.out.println("Original List : \n" + mylist); Collections.shuffle(mylist); System.out.println("\nShuffled List : \n" + mylist); }} |
Output:
Original List : [ide, quiz, neveropen, quiz, practice, qa] Shuffled List : [ide, practice, quiz, qa, neveropen, quiz]
- Shuffling a list using user provided Random Object
Syntax:
Collections.shuffle(list, Random object);
Examples:
Java
// Java program to demonstrate working of shuffle()// with user provided source of randomness.import java.util.*;public class GFG { public static void main(String[] args) { ArrayList<String> mylist = new ArrayList<String>(); mylist.add("ide"); mylist.add("quiz"); mylist.add("neveropen"); mylist.add("quiz"); mylist.add("practice"); mylist.add("qa"); System.out.println("Original List : \n" + mylist); // Here we use Random() to shuffle given list. Collections.shuffle(mylist, new Random()); System.out.println("\nShuffled List with Random() : \n" + mylist); // Here we use Random(3) to shuffle given list. Here 3 // is seed value for Random. Collections.shuffle(mylist, new Random(3)); System.out.println("\nShuffled List with Random(3) : \n" + mylist); // Here we use Random(5) to shuffle given list. Here 5 // is seed value for Random. Collections.shuffle(mylist, new Random(5)); System.out.println("\nShuffled List with Random(5) : \n" + mylist); }} |
Output:
Original List : [ide, quiz, neveropen, quiz, practice, qa] Shuffled List with Random() : [neveropen, practice, qa, ide, quiz, quiz] Shuffled List with Random(3) : [quiz, ide, practice, quiz, neveropen, qa] Shuffled List with Random(5) : [ide, quiz, neveropen, quiz, practice, qa]
- How to write our own Shuffle method?
We can use Fisher–Yates shuffle Algorithm that works in O(n) time.
Java
// Java Program to shuffle a given arrayimport java.util.Random;import java.util.Arrays;public class ShuffleRand{ // A Function to generate a random permutation of arr[] static void randomize( int arr[], int n) { // Creating a object for Random class Random r = new Random(); // Start from the last element and swap one by one. We don't // need to run for the first element that's why i > 0 for (int i = n-1; i > 0; i--) { // Pick a random index from 0 to i int j = r.nextInt(i); // Swap arr[i] with the element at random index int temp = arr[i]; arr[i] = arr[j]; arr[j] = temp; } // Prints the random array System.out.println(Arrays.toString(arr)); } // Driver Program to test above function public static void main(String[] args) { int[] arr = {1, 2, 3, 4, 5, 6, 7, 8}; int n = arr.length; randomize (arr, n); }} |
Output:
[5, 7, 1, 3, 6, 8, 4, 2]
