[LeetCode] Shuffle an Array

Problem

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();

Solution

class Solution {
    private int[] nums;
    public Solution(int[] nums) {
        this.nums = nums;
    }

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

    /** Returns a random shuffling of the array. */
    public int[] shuffle() {
        int[] rand = new int[nums.length];
        for (int i = 0; i < nums.length; i++) {
            //we shuffle the array by getting random index j
            //which is less than current index i,
            //and swap their values
            int j = (int) (Math.random()* (i+1)); //(i+1) is the range
            rand[i] = rand[j];
            rand[j] = nums[i];
        }
        return rand;
    }
}

/**
 * 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();
 */