Shuffle-an-Array

384. Shuffle an Array

Description

Given an integer array nums, design an algorithm to randomly shuffle the array.

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 will be made to reset and shuffle.

Solutions

Python3

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()

Java

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();
 */

C++

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();
 */

Go

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();
 */

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