Shuffle an Array — LeetCode 384 Python Solution

The problem

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.

Example

Input

["Solution", "shuffle", "reset", "shuffle"]

Output

[null, [3, 1, 2], [1, 2, 3], [1, 3, 2]]

Explanation

Solution solution = new Solution([1, 2, 3]);

Python solution

class Solution:
    def __init__(self, nums: List[int]):
        self.nums = nums
        self.original = nums.copy()

    def reset(self) -> List[int]:
        self.nums = self.original.copy()
        return self.nums

    def shuffle(self) -> List[int]:
        for i in range(len(self.nums)):
            j = random.randrange(i, len(self.nums))
            self.nums[i], self.nums[j] = self.nums[j], self.nums[i]
        return self.nums


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

Complexity

Pattern: Math and Number Theory

Find the closed form, the invariant, or the modular identity — and skip the loop entirely. LeetCode 384. Shuffle an Array is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Math.

The math and number theory guide has the Python template for the pattern and the 485 LeetCode problems that use it.

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