705. Design HashSet.md

705. Design HashSet

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leetcode Daily Challenge on August 2nd, 2020.

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Difficulty : Easy

Related Topics : HashTable、Design

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Design a HashSet without using any built-in hash table libraries.

To be specific, your design should include these functions:

• add(value): Insert a value into the HashSet.
• contains(value) : Return whether the value exists in the HashSet or not.
• remove(value): Remove a value in the HashSet. If the value does not exist in the HashSet, do nothing.

Example:

MyHashSet hashSet = new MyHashSet();
hashSet.add(1);
hashSet.add(2);
hashSet.contains(1);    // returns true
hashSet.contains(3);    // returns false (not found)
hashSet.add(2);
hashSet.contains(2);    // returns true
hashSet.remove(2);
hashSet.contains(2);    // returns false (already removed)

Note:

• All values will be in the range of [0, 1000000].
• The number of operations will be in the range of [1, 10000].
• Please do not use the built-in HashSet library.

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Solution

• mine
  • Java
    • Runtime: 12 ms, faster than 84.08%, Memory Usage: 47.4 MB, less than 51.38% of Java online submissions

      // add/remove/contains O(1)time
      // add/remove/contains O(1)space
      HashMap<Integer,Object> map;
      /** Initialize your data structure here. */
      Object value = new Object();
      public MyHashSet() {
          map = new HashMap<>();
      }
      
      public void add(int key) {
          map.put(key, value);
      }
      
      public void remove(int key) {
          if(map.containsKey(key)) map.remove(key);
      }
      
      /** Returns true if this set contains the specified element */
      public boolean contains(int key) {
          return map.containsKey(key);
      }
      

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