384. Shuffle an Array

Description

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.

Constraints

• 1 <= nums.length <= 200

• -106 <= nums[i] <= 106

• All the elements of nums are unique.

• At most 5 * 104 calls in total will be made to reset and shuffle.

Approach

Links

• Binarysearch

• GeeksforGeeks

• Leetcode

• ProgramCreek

• YouTube

Examples

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]

Solutions

Solution 1

/**
 * Time complexity : 
 * Space complexity : 
 */

class Solution {
    private static final Random random = new Random();
    private final int arrLen;
    private int[] original, shuffled;

    public Solution(int[] nums) {
        arrLen = nums.length;
        original = nums;
        shuffled = Arrays.copyOf(original, arrLen);
    }
    
    /** Resets the array to its original configuration and return it. */
    public int[] reset() {
        shuffled = Arrays.copyOf(original, arrLen);
        return shuffled;
    }
    
    /** Returns a random shuffling of the array. */
    public int[] shuffle() {
        for(int i = 0; i < arrLen; i++) {
            int index = random.nextInt(arrLen-i) + i;
            int temp = shuffled[index];
            shuffled[index] = shuffled[i];
            shuffled[i] = temp;
        }
        return shuffled;
    }
}

/**
 * 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();
 */

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