384. Shuffle an Array

Leetcode Sort

Shuffle a set of numbers without duplicates.

Example:

// Init an array with set 1, 2, and 3.
int[] nums = {1,2,3};
Solution solution = new Solution(nums);

// Shuffle the array [1,2,3] and return its result. Any permutation of [1,2,3] must equally likely to be returned.
solution.shuffle();

// Resets the array back to its original configuration [1,2,3].
solution.reset();

// Returns the random shuffling of array [1,2,3].
solution.shuffle();

分析

非常简单。既然要shuffle，肯定想到的是Knuth shuffle，然后题目里说还有个reset功能，那就要保留原来的数组。

public class Q384ShuffleAnArray {
    private int[] array;
    private Random random;

    public Q384ShuffleAnArray(int[] nums) {
        this.array = nums;
        random = new Random();

    }

    /** Resets the array to its original configuration and return it. */
    public int[] reset() {
        return array;
    }

    /** Returns a random shuffling of the array. */
    public int[] shuffle() {
        int[] nums = this.array.clone();
        int r, temp;
        for (int i = 0; i < nums.length; i++) {
            //In iteration i, pick integer r between 0 and i uniformly at random.
            r = random.nextInt(i+1);
            // Swap a[i] and a[r].
            temp = nums[i];
            nums[i] = nums[r];
            nums[r] = temp;
        }
        return nums;
    }
}