solve 380.insert-delete-get-random-o-1

Author: andavid

vscode/380.insert-delete-get-random-o-1.java

@@ -0,0 +1,109 @@
+/*
+ * @lc app=leetcode id=380 lang=java
+ *
+ * [380] Insert Delete GetRandom O(1)
+ *
+ * https://leetcode.com/problems/insert-delete-getrandom-o1/description/
+ *
+ * algorithms
+ * Medium (41.99%)
+ * Likes:    1152
+ * Dislikes: 90
+ * Total Accepted:    117.7K
+ * Total Submissions: 273.9K
+ * Testcase Example:  '["RandomizedSet","insert","remove","insert","getRandom","remove","insert","getRandom"]\n[[],[1],[2],[2],[],[1],[2],[]]'
+ *
+ * Design a data structure that supports all following operations in average
+ * O(1) time.
+ *
+ *
+ *
+ * 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:
+ *
+ * // Init an empty set.
+ * RandomizedSet randomSet = new RandomizedSet();
+ *
+ * // Inserts 1 to the set. Returns true as 1 was inserted successfully.
+ * randomSet.insert(1);
+ *
+ * // Returns false as 2 does not exist in the set.
+ * randomSet.remove(2);
+ *
+ * // Inserts 2 to the set, returns true. Set now contains [1,2].
+ * randomSet.insert(2);
+ *
+ * // getRandom should return either 1 or 2 randomly.
+ * randomSet.getRandom();
+ *
+ * // Removes 1 from the set, returns true. Set now contains [2].
+ * randomSet.remove(1);
+ *
+ * // 2 was already in the set, so return false.
+ * randomSet.insert(2);
+ *
+ * // Since 2 is the only number in the set, getRandom always return 2.
+ * randomSet.getRandom();
+ *
+ *
+ */
+class RandomizedSet {
+
+  List<Integer> list;
+  Map<Integer, Integer> map;
+  Random random;
+
+  /** Initialize your data structure here. */
+  public RandomizedSet() {
+    list = new ArrayList<>();
+    map = new HashMap<>();
+    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 (map.containsKey(val)) {
+      return false;
+    }
+    map.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 (!map.containsKey(val)) {
+      return false;
+    }
+    int index = map.get(val);
+    if (index < list.size() - 1) {
+      int last = list.get(list.size() - 1);
+      map.put(last, index);
+      list.set(index, last);
+    }
+    map.remove(val);
+    list.remove(list.size() - 1);
+    return true;
+  }
+
+  /** Get a random element from the set. */
+  public int getRandom() {
+    int index = random.nextInt(list.size());
+    return list.get(index);
+  }
+}
+
+/**
+ * Your RandomizedSet object will be instantiated and called as such:
+ * RandomizedSet obj = new RandomizedSet();
+ * boolean param_1 = obj.insert(val);
+ * boolean param_2 = obj.remove(val);
+ * int param_3 = obj.getRandom();
+ */
+