384. Shuffle an Array

Problem

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

• -10^6 <= nums[i] <= 10^6

• All the elements of nums are unique.

• At most 10^4 calls in total will be made to reset and shuffle.

Solution (Java)

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

    public Solution(int[] nums) {
        this.nums = nums;
        this.random = new Random();
    }

    // Resets the array to its original configuration and return it.
    public int[] reset() {
        return this.nums;
    }

    // Returns a random shuffling of the array.
    public int[] shuffle() {
        int[] shuffled = this.nums.clone();
        for (int i = nums.length - 1; i > 0; i--) {
            int j = random.nextInt(i + 1);
            swap(shuffled, i, j);
        }
        return shuffled;
    }

    private void swap(int[] shuffled, int i, int j) {
        int tmp = shuffled[i];
        shuffled[i] = shuffled[j];
        shuffled[j] = tmp;
    }
}

/**
 * Your Solution object will be instantiated and called as such:
 * Solution obj = new Solution(nums);
 * int[] param_1 = obj.reset();
 * int[] param_2 = obj.shuffle();
 */

Solution (Javascript)

/**
 * @param {number[]} nums
 */
var Solution = function(nums) {
  this.orignalNums = [...nums]
  this.nums = [...nums]
};

/**
 * @return {number[]}
 */
Solution.prototype.reset = function() {
  this.nums = [...this.orignalNums]
  return this.nums
};

/**
 * @return {number[]}
 */
Solution.prototype.shuffle = function() {
  for (let i = 0; i < this.nums.length; i++) {
    const j = getRandomInt(i, this.nums.length)
    ;[this.nums[i], this.nums[j]] = [this.nums[j], this.nums[i]]
  }
  return this.nums
};

function getRandomInt(min, max) {
  return Math.floor(Math.random() * (max - min) + min)
}
/** 
 * Your Solution object will be instantiated and called as such:
 * var obj = new Solution(nums)
 * var param_1 = obj.reset()
 * var param_2 = obj.shuffle()
 */

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).