[LC] 384. Shuffle an Array

Posted 2021-03-16 xuanlu

Shuffle a set of numbers without duplicates.

Example:

// Init an array with set 1, 2, and 3.
int[] nums = {1,2,3};
Solution solution = new Solution(nums);

// Shuffle the array [1,2,3] and return its result. Any permutation of [1,2,3] must equally likely to be returned.
solution.shuffle();

// Resets the array back to its original configuration [1,2,3].
solution.reset();

// Returns the random shuffling of array [1,2,3].
solution.shuffle();

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

/**
 * 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();
 */