completed design-1

MinStack.java

@@ -0,0 +1,47 @@
+// Time Complexity : O(1) for all push pop top getMin
+// Space Complexity : O(n) where n is the number of elements in the stack
+// Did this code successfully run on Leetcode : yes
+// Any problem you faced while coding this : none
+
+// Your code here along with comments explaining your approach
+//used two stacks, one for storing elements and one for storing the minimum element at each position. 
+import java.util.Stack;
+class MinStack 
+{
+    private Stack<Integer> stack;
+    private Stack<Integer> minStack;
+
+    public MinStack() 
+    {
+        stack = new Stack<>();
+        minStack = new Stack<>();
+    }
+
+    public void push(int val) 
+    {
+        stack.push(val);
+        if (minStack.isEmpty() || val <= minStack.peek()) 
+        {
+            minStack.push(val);
+        } else 
+        {
+            minStack.push(minStack.peek());
+        }
+    }
+
+    public void pop() 
+    {
+        stack.pop();
+        minStack.pop();
+    }
+
+    public int top() 
+    {
+        return stack.peek();
+    }
+
+    public int getMin() 
+    {
+        return minStack.peek();
+    }
+}

README.md

@@ -6,8 +6,7 @@ Explain your approach in **three sentences only** at top of your code
 
 
 
-## Problem 2:
-Design MinStack (https://leetcode.com/problems/min-stack/)
+## Problem 2: Design MinStack (https://leetcode.com/problems/min-stack/)
 
 
 

design_hashset.java

@@ -0,0 +1,53 @@
+// Time Complexity : O(1) for add, remove and contains operations
+// Space Complexity : O(n) where n is the number of elements in the hash set
+// Did this code successfully run on Leetcode : yes
+// Any problem you faced while coding this : none
+
+// Your code here along with comments explaining your approach
+//used bucketing to split each key in two parts: key % 1000 gives the bucket index, and key / 1000 gives the position inside that bucket.  
+
+class MyHashSet {
+    private boolean[][] storage;
+    private int buckets;
+    private int bucketItems;
+
+    public MyHashSet() {
+        this.buckets = 1000;
+        this.bucketItems = 1001;
+        this.storage = new boolean[buckets][];
+    }
+
+    private int hash(int key) {
+        return key % buckets;
+    }
+
+    private int pos(int key) {
+        return key / buckets;
+    }
+
+    public void add(int key) {
+        int bucket = hash(key);
+        int bucketItem = pos(key);
+
+        if (storage[bucket] == null) {
+            storage[bucket] = new boolean[bucketItems];
+        }
+        storage[bucket][bucketItem] = true;
+    }
+
+    public void remove(int key) {
+        int bucket = hash(key);
+        int bucketItem = pos(key);
+
+        if (storage[bucket] != null) {
+            storage[bucket][bucketItem] = false;
+        }
+    }
+
+    public boolean contains(int key) {
+        int bucket = hash(key);
+        int bucketItem = pos(key);
+
+        return storage[bucket] != null && storage[bucket][bucketItem];
+    }
+}