_384.java

package com.fishercoder.solutions;
/**
 * 384. Shuffle an Array
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();*/
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;
import java.util.Random;

public class _384 {

    public static class Solution1 {
        //Note: the problem states that this is a set without duplicates which makes building all combinations easier

        private List<List<Integer>> combinations;
        private int[] original;
        private Random random;

        public Solution1(int[] nums) {
            original = nums;
            random = new Random();
            combinations = buildAllComb(nums);
        }

        //insert next value into all possible positions, I wrote this method myself, of course it could be simplified to not use a queue
        //but it just naturally came into my mind that I used a queue
        private List<List<Integer>> buildAllComb(int[] nums) {
            List<List<Integer>> result = new ArrayList();
            if (nums == null || nums.length == 0) {
                return result;
            }

            List<Integer> list = new ArrayList<Integer>();
            list.add(nums[0]);
            Queue<List<Integer>> q = new LinkedList();
            q.offer(list);
            for (int i = 1; i < nums.length; i++) {
                int qSize = q.size();
                for (int k = 0; k < qSize; k++) {
                    List<Integer> currList = q.poll();
                    for (int j = 0; j <= currList.size(); j++) {
                        List<Integer> newL = new ArrayList<Integer>(currList);
                        newL.add(j, nums[i]);
                        q.offer(newL);
                    }
                }
            }
            while (!q.isEmpty()) {
                result.add(q.poll());
            }
            return result;
        }

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

        /**
         * Returns a random shuffling of the array.
         */
        public int[] shuffle() {
            if (original == null || original.length == 0) {
                return original;
            }
            int randomIndex = random.nextInt(combinations.size());
            List<Integer> list = combinations.get(randomIndex);
            int[] result = new int[list.size()];
            for (int i = 0; i < list.size(); i++) {
                result[i] = list.get(i);
            }
            return result;
        }
    }
}