384. Shuffle an Array

1. Question

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.

2. Examples

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]

3. Constraints

  • 1 <= nums.length <= 200
  • -106 <= nums[i] <= 106
  • All the elements of nums are unique.
  • At most 5 104 calls *in total will be made to reset and shuffle.

4. References

来源:力扣(LeetCode) 链接:https://leetcode-cn.com/problems/shuffle-an-array 著作权归领扣网络所有。商业转载请联系官方授权,非商业转载请注明出处。

5. Solutions

class Solution {

  int[] nums;
  int[] shuffle;
  Random random;

  public Solution(int[] nums) {
    this.nums = nums;
    random = new Random();
  }

  public int[] reset() {
    return nums;
  }

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

  private void swap(int a, int b) {
    int temp = shuffle[a];
    shuffle[a] = shuffle[b];
    shuffle[b] = 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();
 */
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