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();

思路：就是第i个元素，跟后面random [0,i]的元素进行互换即可，

注意Random random = new Random(); random.nextInt(i+1) [0,i]

class Solution {
    private int[] original;
    private int[] A;
    private Random random;
    public Solution(int[] nums) {
        int n = nums.length;
        this.original = new int[n];
        this.A = new int[n];
        for(int i = 0; i < nums.length; i++) {
            original[i] = nums[i];
            A[i] = nums[i];
        }
        this.random = new Random();
    }
    
    public int[] reset() {
        return this.original;
    }
    
    public int[] shuffle() {
        for(int i = original.length - 1; i >= 0; i--) {
            int index = random.nextInt(i + 1);
            swap(A, index, i);
        }
        return A;
    }
    
    private void swap(int[] A, int i, int j) {
        int temp = A[i];
        A[i] = A[j];
        A[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();
 */