384. Shuffle an Array

Description

Shuffle a set of numbers without duplicates.

Example:

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();

Solution

Random

经典的shuffle算法，随机&交换。注意random.nextInt(n)返回值是[0, n)范围内的随机值。

class Solution {
    private int[] nums;
    private Random random;
    
    public Solution(int[] nums) {
        this.nums = nums;
        random = new Random();
    }
    
    /** Resets the array to its original configuration and return it. */
    public int[] reset() {
        return nums;
    }
    
    /** Returns a random shuffling of the array. */
    public int[] shuffle() {
        int[] shuffle = nums.clone();
        
        for (int i = shuffle.length; i > 0; --i) {
            int j = (int) random.nextInt(i);    // returns x between [0, i)
            swap(shuffle, j, i - 1);
        }
        
        return shuffle;
    }
    
    private void swap(int[] nums, int i, int j) {
        int tmp = nums[i];
        nums[i] = nums[j];
        nums[j] = tmp;
    }
}

/**
 * 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();
 */