0384 - Shuffle an Array

0384 - 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.

Examples

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 <= 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.

Java Solution

class Solution {
    
    private int[] nums;
    private int[] original;
    
    Random rand = new Random();

    public Solution(int[] nums) {
        this.nums = nums;
        original = nums.clone();
    }
    
    public int[] reset() {
        this.nums = original;
        original = original.clone();
        return original;
    }
    
    public int[] shuffle() {
        for(int i = 0; i < this.nums.length; i++) {
            swap(i, rand.nextInt(this.nums.length - i) + i);
        }
        return this.nums;
    }
    
    private void swap(int i, int j) {
        int temp = this.nums[i];
        this.nums[i] = this.nums[j];
        this.nums[j] = temp;        
    }
}

/**
 * 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();
 */