384 Shuffle an Array 打乱数组

Description:
Given an integer array nums, design an algorithm to randomly shuffle the array.

Implement the Solution class:

Solution(int[] nums) Initializes the object with the integer array nums.
int[] reset() Resets the array to its original configuration and returns it.
int[] shuffle() Returns a random shuffling of the array.

Example:

Example 1:

Input
["Solution", "shuffle", "reset", "shuffle"]
[[[1, 2, 3]], [], [], []]
Output
[null, [3, 1, 2], [1, 2, 3], [1, 3, 2]]

Explanation

Solution solution = new Solution([1, 2, 3]);
solution.shuffle();    // Shuffle the array [1,2,3] and return its result. Any permutation of [1,2,3] must be equally likely to be returned. Example: return [3, 1, 2]
solution.reset();      // Resets the array back to its original configuration [1,2,3]. Return [1, 2, 3]
solution.shuffle();    // Returns the random shuffling of array [1,2,3]. Example: return [1, 3, 2]

Constraints:

1 <= nums.length <= 200
-10^6 <= nums[i] <= 10^6
All the elements of nums are unique.
At most 5 * 10^4 calls will be made to reset and shuffle.

题目描述:
给你一个整数数组 nums ，设计算法来打乱一个没有重复元素的数组。

实现 Solution class:

Solution(int[] nums) 使用整数数组 nums 初始化对象
int[] reset() 重设数组到它的初始状态并返回
int[] shuffle() 返回数组随机打乱后的结果

示例 :

输入
["Solution", "shuffle", "reset", "shuffle"]
[[[1, 2, 3]], [], [], []]
输出
[null, [3, 1, 2], [1, 2, 3], [1, 3, 2]]

解释

Solution solution = new Solution([1, 2, 3]);
solution.shuffle();    // 打乱数组 [1,2,3] 并返回结果。任何 [1,2,3]的排列返回的概率应该相同。例如，返回 [3, 1, 2]
solution.reset();      // 重设数组到它的初始状态 [1, 2, 3] 。返回 [1, 2, 3]
solution.shuffle();    // 随机返回数组 [1, 2, 3] 打乱后的结果。例如，返回 [1, 3, 2]

提示：

1 <= nums.length <= 200
-10^6 <= nums[i] <= 10^6
nums 中的所有元素都是 唯一的
最多可以调用 5 * 10^4 次 reset 和 shuffle

思路:

洗牌的时候每次选择一个随机数, 进行交换
reset()时间复杂度O(1), shuffle()时间复杂度O(n), 空间复杂度O(n)

代码:
C++:

class Solution 
{
public:
    Solution(vector<int>& nums) 
    {
        v = nums;
    }
    
    /** Resets the array to its original configuration and return it. */
    vector<int> reset() 
    {
        return v;
    }
    
    /** Returns a random shuffling of the array. */
    vector<int> shuffle() 
    {
        vector<int> result = v;
        for (int i = 1; i < result.size(); i++)
        {
            int r = rand() % (i + 1);
            if (r != i) swap(result[r], result[i]);
        }
        return result;
    }
private:
    vector<int> v;
};

/**
 * Your Solution object will be instantiated and called as such:
 * Solution* obj = new Solution(nums);
 * vector<int> param_1 = obj->reset();
 * vector<int> param_2 = obj->shuffle();
 */

Java:

class Solution {

    private int[] nums;
    private Random random;
    
    public Solution(int[] nums) {
        this.nums = nums;
        this.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() {
        int[] result = Arrays.copyOf(nums, nums.length);
        for (int i = 1; i < nums.length; i++) {
            int r = random.nextInt(i + 1);
            if (r != i) swap(result, r, i);
        }
        return result;
    }
    
    private void swap(int[] result, int i, int j) {
        int temp = result[i];
        result[i] = result[j];
        result[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();
 */

Python:

class Solution:

    def __init__(self, nums: List[int]):
        self.nums = nums
        

    def reset(self) -> List[int]:
        """
        Resets the array to its original configuration and return it.
        """
        return self.nums


    def shuffle(self) -> List[int]:
        """
        Returns a random shuffling of the array.
        """
        result = self.nums[:]
        for i in range(1, len(result)):
            r = random.randrange(i + 1)
            if r != i:
                result[i], result[r] = result[r], result[i]
        return result



# Your Solution object will be instantiated and called as such:
# obj = Solution(nums)
# param_1 = obj.reset()
# param_2 = obj.shuffle()