Shuffle an Array

Problem

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
• -10^6 <= nums[i] <= 10^6
• All the elements of nums are unique.
• At most 10^4 calls in total will be made to reset and shuffle.

Hint #1

The solution expects that we always use the original array to shuffle() else some of the test cases fail. (Credits; @snehasingh31)

Solution

Code

C++

#include <vector>
#include <iostream>
using namespace std;

class Solution
{
private:
    vector<int> origin;

public:
    Solution(vector<int> &nums) : origin(nums)
    {
        //origin = nums;
    }

    vector<int> reset()
    {
        return origin;
    }

    vector<int> shuffle1()
    {
        vector<int> shuffled = origin;
        int last = shuffled.size();
        for (int i = shuffled.size() - 1; i >= 0; i--)
        {
            int ptr = rand() % last;
            swap(shuffled[i], shuffled[ptr]);
            last--;
        }
        return shuffled;
    }
    
    vector<int> shuffle2()
    {
        vector<int> shuffled = origin;
        for (int i = shuffled.size() - 1; i > 0; --i) {
        int j = rand() % (i + 1);
        swap(shuffled[i], shuffled[j]);
        }
    return shuffled;
    }
};
/**
 * 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();
 */