LeetCode 384: Shuffle an Array Solution

Master LeetCode problem 384 (Shuffle an Array), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

384. Shuffle an Array

Medium

Array Math Design Randomized

Problem Explanation

Explanation

To shuffle an array such that all permutations are equally likely, we can use the Fisher-Yates algorithm. The idea is to iterate over the array from the end to the beginning, and at each iteration, swap the current element with a randomly selected element from the remaining elements.

For the shuffle method, we create a copy of the original array and apply the Fisher-Yates shuffle algorithm to shuffle the elements.
For the reset method, we return a copy of the original array to reset it back to its initial configuration.

Time Complexity:

shuffle: O(n)
reset: O(n)

Space Complexity: O(n), where n is the number of elements in the input array.

Solution Code

import java.util.Arrays;
import java.util.Random;

class Solution {
    private int[] original;
    private int[] shuffled;
    private Random rand;

    public Solution(int[] nums) {
        original = nums.clone();
        shuffled = nums.clone();
        rand = new Random();
    }

    public int[] reset() {
        return original;
    }

    public int[] shuffle() {
        for (int i = shuffled.length - 1; i > 0; i--) {
            int j = rand.nextInt(i + 1);
            swap(shuffled, i, j);
        }
        return shuffled;
    }

    private void swap(int[] arr, int i, int j) {
        int temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
    }
}

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