384. Shuffle an Array

题目分析

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这道题目要求我们完善 shuffle 方法，将一个数组进行乱序操作，同时要求我们完善 reset 方法，这个方法能够返回原数组。

代码

class Solution {
    
    private int[] nums;
    private int[] res;
    private Random random;

    public Solution(int[] nums) {
        this.nums = nums;
        res = Arrays.copyOf(nums, nums.length);
        random = new Random();
    }
    
    /** 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() {
        if(res == null) {
            return null;
        } else {
            for(int i = 1; i < res.length; i++) {
                // 从 0 ~ i 下标中任选一个位置和当前位置的值进行交换 
                int j = random.nextInt(i + 1);
                swap(res, i, j);
            }
            return res;
        }
    }
    
    private void swap(int[] res, int i, int j) {
        int temp = res[i];
        res[i] = res[j];
        res[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();
 */