384. Shuffle an Array

Given an integer array nums, design an algorithm to randomly shuffle the array. All permutations of the array should be equally likely as a result of the shuffling.

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 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]

思路Coding化:

class Solution:

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

    def reset(self) -> List[int]:
        return self.arr

    def shuffle(self) -> List[int]:
        ans = self.arr.copy()
        for i in range(len(ans)):
            # Fisher-Yates Algorithm
            # 從剩下的數隨機抽取並與當前數字交換
            swp_num = random.randrange(i, len(ans)) 
            ans[i],ans[swp_num] = ans[swp_num], ans[i]
        return ans

Time Complexity: O(n)

Space Complexity: O(n)