Shuffle an Array LeetCode Solution

Problem – Shuffle an Array

Given an integer array nums, design an algorithm to randomly shuffle the array. All permutations of the array should be equally likely as a result of the shuffling.

Implement the Solution class:

• Solution(int[] nums) Initializes the object with the integer array nums.
• int[] reset() Resets the array to its original configuration and returns it.
• int[] shuffle() Returns a random shuffling of the array.

Example 1:

Input
["Solution", "shuffle", "reset", "shuffle"]
[[[1, 2, 3]], [], [], []]
Output
[null, [3, 1, 2], [1, 2, 3], [1, 3, 2]]

Explanation
Solution solution = new Solution([1, 2, 3]);
solution.shuffle();    // Shuffle the array [1,2,3] and return its result.
                       // Any permutation of [1,2,3] must be equally likely to be returned.
                       // Example: return [3, 1, 2]
solution.reset();      // Resets the array back to its original configuration [1,2,3]. Return [1, 2, 3]
solution.shuffle();    // Returns the random shuffling of array [1,2,3]. Example: return [1, 3, 2]

Constraints:

• 1 <= nums.length <= 50
• -106 <= nums[i] <= 106
• All the elements of nums are unique.
• At most 104 calls in total will be made to reset and shuffle.

Shuffle an Array LeetCode Solution in Java

import java.util.Random;

public class Solution {
    private int[] nums;
    private Random random;

    public Solution(int[] nums) {
        this.nums = nums;
        random = new Random();
    }
    
    /** Resets the array to its original configuration and return it. */
    public int[] reset() {
        return nums;
    }
    
    /** Returns a random shuffling of the array. */
    public int[] shuffle() {
        if(nums == null) return null;
        int[] a = nums.clone();
        for(int j = 1; j < a.length; j++) {
            int i = random.nextInt(j + 1);
            swap(a, i, j);
        }
        return a;
    }
    
    private void swap(int[] a, int i, int j) {
        int t = a[i];
        a[i] = a[j];
        a[j] = t;
    }
}

Shuffle an Array LeetCode Solution in Python

class Solution(object):
    def __init__(self, nums):
        self.reset = lambda: nums
        self.shuffle = lambda: random.sample(nums, len(nums))

Shuffle an Array LeetCode Solution in C++

class Solution {
    vector<int> nums;
public:
    Solution(vector<int> nums) {
        this->nums = nums;
    }
    
    /** Resets the array to its original configuration and return it. */
    vector<int> reset() {
        return nums;
    }
    
    /** Returns a random shuffling of the array. */
    vector<int> shuffle() {
        vector<int> result(nums);
        for (int i = 0;i < result.size();i++) {
            int pos = rand()%(result.size()-i);
            swap(result[i+pos], result[i]);
        }
        return result;
    }
};

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