add 705

Author: fishercoder1534

README.md

@@ -100,6 +100,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |713|[Subarray Product Less Than K](https://leetcode.com/problems/subarray-product-less-than-k/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_713.java) | O(n) | O(1) | |Medium |
 |712|[Minimum ASCII Delete Sum for Two Strings](https://leetcode.com/problems/minimum-ascii-delete-sum-for-two-strings/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_712.java) | O(m*n) | O(m*n) | |Medium | DP
 |709|[To Lower Case](https://leetcode.com/problems/to-lower-case/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_709.java) | O(n) | O(1) | |Easy| String
+|705|[Design HashSet](https://leetcode.com/problems/design-hashset/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_705.java) | O(1) | O(n) | |Easy| Design
 |704|[Binary Search](https://leetcode.com/problems/binary-search/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_704.java) | O(logn) | O(1) | |Easy| Binary Search
 |699|[Falling Squares](https://leetcode.com/problems/falling-squares/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_699.java) | O(n^2) | O(n) | |Hard | Segment Tree
 |698|[Partition to K Equal Sum Subsets](https://leetcode.com/problems/partition-to-k-equal-sum-subsets/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_698.java) | O(n*(2^n)) | O(2^n) | |Medium | Backtracking

src/main/java/com/fishercoder/solutions/_705.java

@@ -0,0 +1,61 @@
+package com.fishercoder.solutions;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * 705. Design HashSet
+ *
+ * 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.
+ */
+public class _705 {
+  public static class Solution1 {
+    class MyHashSet {
+      Map<Integer, Integer> map;
+
+      /** Initialize your data structure here. */
+      public MyHashSet() {
+        map = new HashMap<>();
+      }
+
+      public void add(int key) {
+        map.put(key, 0);
+      }
+
+      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);
+      }
+    }
+  }
+}