Leetcode 384 - Shuffle an array

Note:

  • How to shuffle randomly?
  • For an array starting from 0 to len - 1.
    • First, pick an index between [0, len - 1] and swap with index 0.
    • Then, pick an index between [1, len - 1] and swap with index 1.
    • Pick an index between [len - 1, len - 1] and swap with index len - 1…
  • Done.

Question:

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:

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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]

Code:
O(N)

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/**
* @param {number[]} nums
*/
var Solution = function(nums) {
this.array = nums;
};

/**
* @return {number[]}
*/
Solution.prototype.reset = function() {
return this.array;
};

/**
* @return {number[]}
*/
Solution.prototype.shuffle = function() {
let res = [...this.array];
for (let i = 0; i < res.length; i++) {
const r = ~~(Math.random() * (res.length - i) + i);
[res[i], res[r]] = [res[r], res[i]];
}
return res;
};

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