0384. Shuffle an Array

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](/kumaeki/LeetCode/wiki/[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
-10^6 <= nums[i] <= 10^6
All the elements of nums are unique.
At most 5 * 10^4 calls in total will be made to reset and shuffle.

解法1

需要打乱顺序时, 遍历每个元素, 随机和数组中的某个元素交换位置(包括它自己).

class Solution {

    int[] original;
    int[] res;
    Random ran;
    
    public Solution(int[] nums) {
        original = nums;
        res = nums.clone();
        ran = new Random();
    }
    
    /** Resets the array to its original configuration and return it. */
    public int[] reset() {
        res = original.clone();
        return res;
    }
    
    /** Returns a random shuffling of the array. */
    public int[] shuffle() {
        for(int i = 0, len = res.length; i < len - 1; i++)
            swap(res, i, i + ran.nextInt(len - i));
        return res;
    }
    
    private void swap(int[] arr, int i, int j){
        int temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
    }
}

/**
 * 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();
 */

0384. Shuffle an Array - kumaeki/LeetCode GitHub Wiki

解法1