shuffle an array

fishercoder1534 · fishercoder1534 · commit c8fe046e2986 · 2016-08-11T20:26:09.000-07:00
diff --git a/MEDIUM/src/medium/ShuffleAnArray.java b/MEDIUM/src/medium/ShuffleAnArray.java
@@ -0,0 +1,93 @@
+package medium;
+/**384. Shuffle an Array  QuestionEditorial Solution  My Submissions
+Total Accepted: 94
+Total Submissions: 247
+Difficulty: Medium
+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 ShuffleAnArray {
+    
+    public static void main(String...strings){
+        int[] nums = new int[]{1,2,3};
+        Solution_for_this_question test = new Solution_for_this_question(nums);
+    }
+
+}
+class Solution_for_this_question {
+    //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 Solution_for_this_question(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<List<Integer>>();
+        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;
+    }
+}
+
