384. Shuffle an Array

Description

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]

Constraints:

1 <= nums.length <= 50
-10⁶ <= nums[i] <= 10⁶
All the elements of nums are unique.
At most 10⁴ calls in total will be made to reset and shuffle.

Solution

shuffle-an-array.py

from random import randint

class Solution:

    def __init__(self, nums: List[int]):
        self.nums = nums
        self.n = len(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.
        """
        res = self.nums[:]

        for i in range(self.n):
            index = randint(i, self.n - 1)
            res[i], res[index] = res[index], res[i]

        return res

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