384. Shuffle an Array

最直观的，直接新建复制数组，i的取值范围：0 到 (size - 1)，随机数random的位置：i后面的所有index，然后交换i和random的位置。

class Solution {

    int[] nums;
    int size;
    Random random;

    public Solution(int[] nums) {
        this.nums = nums;
        this.size = nums.length;
        this.random = new Random();
    }

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

    /** Returns a random shuffling of the array. */
    public int[] shuffle() {
        int[] copy = Arrays.copyOf(this.nums, this.size);
        for (int i = 0; i < this.size - 1; i++) {
            int randomIndex = (int) this.random.nextInt(this.size - i) + i;
            int tmp = copy[i];
            copy[i] = copy[randomIndex];
            copy[randomIndex] = tmp;   
        }
        return copy;
    }
}