# Leetcode 384. Shuffle an Array

2 min readJul 20, 2021

[medium]

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 <= 200`

`-106 <= nums[i] <= 106`

- All the elements of
`nums`

are**unique**. - At most
`5 * 104`

calls**in total**will be made to`reset`

and`shuffle`

.

[Java] (from @2499370956)

- I don’t really know clone function, so I create a global variable to store original array. If I want to refresh the array, it will return the original array
- Using “Math.random()” function to get a random 0 < x ≤ 1 function times i +1 to avoid overflow.
- Swap the current new array location to somewhere else, and put the number into the new location, which we get it from Random function.
- step will be: assign new array -> get random factor -> swap the location