Question

384. Shuffle an Array

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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.

Solutions

Solution 1

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()

class Solution {
  private int[] nums;
  private int[] original;
  private Random rand;

  public Solution(int[] nums) {
    this.nums = nums;
    this.original = Arrays.copyOf(nums, nums.length);
    this.rand = new Random();
  }

  public int[] reset() {
    nums = Arrays.copyOf(original, original.length);
    return nums;
  }

  public int[] shuffle() {
    for (int i = 0; i < nums.length; ++i) {
      swap(i, i + rand.nextInt(nums.length - i));
    }
    return nums;
  }

  private void swap(int i, int j) {
    int t = nums[i];
    nums[i] = nums[j];
    nums[j] = t;
  }
}

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

class Solution {
public:
  vector<int> nums;
  vector<int> original;

  Solution(vector<int>& nums) {
    this->nums = nums;
    this->original.resize(nums.size());
    copy(nums.begin(), nums.end(), original.begin());
  }

  vector<int> reset() {
    copy(original.begin(), original.end(), nums.begin());
    return nums;
  }

  vector<int> shuffle() {
    for (int i = 0; i < nums.size(); ++i) {
      int j = i + rand() % (nums.size() - i);
      swap(nums[i], nums[j]);
    }
    return nums;
  }
};

/**
 * Your Solution object will be instantiated and called as such:
 * Solution* obj = new Solution(nums);
 * vector<int> param_1 = obj->reset();
 * vector<int> param_2 = obj->shuffle();
 */

type Solution struct {
  nums, original []int
}

func Constructor(nums []int) Solution {
  return Solution{nums, append([]int(nil), nums...)}
}

func (this *Solution) Reset() []int {
  copy(this.nums, this.original)
  return this.nums
}

func (this *Solution) Shuffle() []int {
  n := len(this.nums)
  for i := range this.nums {
    j := i + rand.Intn(n-i)
    this.nums[i], this.nums[j] = this.nums[j], this.nums[i]
  }
  return this.nums
}

/**
 * Your Solution object will be instantiated and called as such:
 * obj := Constructor(nums);
 * param_1 := obj.Reset();
 * param_2 := obj.Shuffle();
 */

class Solution {
  private nums: number[];

  constructor(nums: number[]) {
    this.nums = nums;
  }

  reset(): number[] {
    return this.nums;
  }

  shuffle(): number[] {
    const n = this.nums.length;
    const res = [...this.nums];
    for (let i = 0; i < n; i++) {
      const j = Math.floor(Math.random() * n);
      [res[i], res[j]] = [res[j], 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()
 */

use rand::Rng;
struct Solution {
  nums: Vec<i32>,
}

/**
 * `&self` means the method takes an immutable reference.
 * If you need a mutable reference, change it to `&mut self` instead.
 */
impl Solution {
  fn new(nums: Vec<i32>) -> Self {
    Self { nums }
  }

  fn reset(&self) -> Vec<i32> {
    self.nums.clone()
  }

  fn shuffle(&mut self) -> Vec<i32> {
    let n = self.nums.len();
    let mut res = self.nums.clone();
    for i in 0..n {
      let j = rand::thread_rng().gen_range(0, n);
      res.swap(i, j);
    }
    res
  }
}/**
 * Your Solution object will be instantiated and called as such:
 * let obj = Solution::new(nums);
 * let ret_1: Vec<i32> = obj.reset();
 * let ret_2: Vec<i32> = obj.shuffle();
 */

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

/**
 * Resets the array to its original configuration and return it.
 * @return {number[]}
 */
Solution.prototype.reset = function () {
  return this.nums;
};

/**
 * Returns a random shuffling of the array.
 * @return {number[]}
 */
Solution.prototype.shuffle = function () {
  let a = this.nums.slice();
  for (let i = 0; i < a.length; i++) {
    let rand = Math.floor(Math.random() * (a.length - i)) + i;
    let tmp = a[i];
    a[i] = a[rand];
    a[rand] = tmp;
  }
  return a;
};

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