384. Shuffle an Array

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 {

    int[] original;
    int[] arr;
    Random rand;
    public Solution(int[] nums) {
        arr = nums;
        original = nums.clone();    
        rand = new Random();
    }
    
    /** Resets the array to its original configuration and return it. */
    public int[] reset() {
        arr = original;
        original = original.clone();
        return original;
    }
    
    /** Returns a random shuffling of the array. */
    public int[] shuffle() {
        for(int i = 0; i < arr.length; i++) {
            swap(arr, i, getInd(i, arr.length));
        }
        return arr;
    }
    
    public void swap(int[] nums, int i, int j) {
        int tmp = nums[i];
        nums[i] = nums[j];
        nums[j] = tmp;
    }
    
    public int getInd(int l, int r) {
        return rand.nextInt(r - l) + l;
    }
}

Fisher-Yates Algorithm

swap current element with the later index element.