Question

Formatted question description: https://leetcode.ca/all/384.html

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.

Algorithm

Traverse each position of the array, randomly generate a coordinate position each time, and then exchange the number of the current traverse position and the randomly generated coordinate position.

If the array has n numbers, then we also randomly exchange n sets of positions, thus achieving the purpose of shuffling.

It should be noted here that i + rand()% (res.size()-i) cannot be written as rand()% res.size().

Code

import java.util.ArrayList;
import java.util.List;
import java.util.Random;

public class Shuffle_an_Array {

    // 1. array deep copy
    // 2. random.nextInt to dynamic list size
    class Solution {
        private int[] array;
        private int[] original;

        private Random rand = new Random();

        private List<Integer> getArrayCopy() {
            List<Integer> asList = new ArrayList<Integer>();
            for (int i = 0; i < array.length; i++) {
                asList.add(array[i]);
            }
            return asList;
        }

        public Solution(int[] nums) {
            array = nums;
            original = nums.clone();
        }

        public int[] reset() {
            array = original;
            original = original.clone();
            return array;
        }

        public int[] shuffle() {
            List<Integer> aux = getArrayCopy();

            for (int i = 0; i < array.length; i++) {
                int removeIdx = rand.nextInt(aux.size());
                array[i] = aux.get(removeIdx);
                aux.remove(removeIdx);
            }

            return array;
        }
    }
/**
 * 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 {
    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();
 */

// OJ: https://leetcode.com/problems/shuffle-an-array/
// Time:
//      Solution: O(N)
//      reset: O(1)
//      shuffle: O(N)
// Space: O(N)
class Solution {
private:
    vector<int> nums;
public:
    Solution(vector<int> nums) : nums(nums) {}
    
    vector<int> reset() {
        return nums;
    }
    
    vector<int> shuffle() {
        vector<int> ans(nums);
        for (int i = nums.size(); i > 1; --i) {
            int j = rand() % i;
            swap(ans[i - 1], ans[j]);
        }
        return ans;
    }
};

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(object):

  def __init__(self, nums):
    """

    :type nums: List[int]
    :type size: int
    """
    self.nums = nums
    self.reset = lambda: self.nums

  def shuffle(self):
    """
    Returns a random shuffling of the array.
    :rtype: List[int]
    """
    nums = self.nums + []
    for i in reversed(range(0, len(nums))):
      idx = random.randrange(0, i + 1)
      nums[i], nums[idx] = nums[idx], nums[i]
    return nums

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

/**
 * @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()
 */

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();
 */

384 - Shuffle an Array

Question

Algorithm

Code

All Problems

All Solutions

Welcome to Subscribe On Youtube

Question

Algorithm

Code

All Problems

All Solutions