Mosand
diff --git a/‎src/main/java/com/fishercoder/solutions/_380.java
Lines changed: 74 additions & 14 deletions b/‎src/main/java/com/fishercoder/solutions/_380.java
Lines changed: 74 additions & 14 deletions
@@ -1,53 +1,113 @@
 package com.fishercoder.solutions;
 
-import java.util.HashMap;
-import java.util.Map;
-import java.util.Random;
+import java.util.*;
 
 /**
  * 380. Insert Delete GetRandom O(1)
  * Design a data structure that supports all following operations in average O(1) time.
- * <p>
+ *
  * insert(val): Inserts an item val to the set if not already present.
  * remove(val): Removes an item val from the set if present.
  * getRandom: Returns a random element from current set of elements. Each element must have the same probability of being returned.
  * Example:
- * <p>
+ *
  * // Init an empty set.
  * RandomizedSet randomSet = new RandomizedSet();
- * <p>
+ *
  * // Inserts 1 to the set. Returns true as 1 was inserted successfully.
  * randomSet.insert(1);
- * <p>
+ *
  * // Returns false as 2 does not exist in the set.
  * randomSet.remove(2);
- * <p>
+ *
  * // Inserts 2 to the set, returns true. Set now contains [1,2].
  * randomSet.insert(2);
- * <p>
+ *
  * // getRandom should return either 1 or 2 randomly.
  * randomSet.getRandom();
- * <p>
+ *
  * // Removes 1 from the set, returns true. Set now contains [2].
  * randomSet.remove(1);
- * <p>
+ *
  * // 2 was already in the set, so return false.
  * randomSet.insert(2);
- * <p>
+ *
  * // Since 2 is the only number in the set, getRandom always return 2.
  * randomSet.getRandom();
  */
 
 public class _380 {
+
+    public static class Solution1 {
+        /**
+         * credit: https://leetcode.com/problems/insert-delete-getrandom-o1/discuss/85401/Java-solution-using-a-HashMap-and-an-ArrayList-along-with-a-follow-up.-(131-ms)
+         */
+        public static class RandomizedSet {
+            Map<Integer, Integer> locationMap;
+            List<Integer> list;
+            Random random;
+
+            /**
+             * Initialize your data structure here.
+             */
+            public RandomizedSet() {
+                locationMap = new HashMap<>();
+                list = new ArrayList<>();
+                random = new Random();
+            }
+
+            /**
+             * Inserts a value to the set. Returns true if the set did not already contain the specified element.
+             */
+            public boolean insert(int val) {
+                if (locationMap.containsKey(val)) {
+                    return false;
+                } else {
+                    locationMap.put(val, list.size());
+                    list.add(val);
+                    return true;
+                }
+            }
+
+            /**
+             * Removes a value from the set. Returns true if the set contained the specified element.
+             */
+            public boolean remove(int val) {
+                if (!locationMap.containsKey(val)) {
+                    return false;
+                } else {
+                    int location = locationMap.get(val);
+                    /**if it's not the last one, then swap the last one with this val*/
+                    if (location < list.size() - 1) {
+                        int lastOne = list.get(list.size() - 1);
+                        list.set(location, lastOne);
+                        locationMap.put(lastOne, location);
+                    }
+                    locationMap.remove(val);
+                    list.remove(list.size() - 1);
+                    return true;
+                }
+            }
+
+            /**
+             * Get a random element from the set.
+             */
+            public int getRandom() {
+                return list.get(random.nextInt(list.size()));
+            }
+
+        }
+    }
+
     /**
      * Your _380 object will be instantiated and called as such:
      * _380 obj = new _380();
      * boolean param_1 = obj.insert(val);
      * boolean param_2 = obj.delete(val);
      * int param_3 = obj.getRandom();
      */
-    public static class Solution1 {
-        //TODO: this is not ideal, optimize it.
+    public static class Solution2 {
+        /**This is not ideal and not meeting average O(1) time for all three operations.*/
         public static class RandomizedSet {
 
             Map<Integer, Integer> forwardMap;