Completed Design-1

MinStack.java

@@ -0,0 +1,85 @@
+// Time Complexity :
+// push(val)  -> O(1)
+// pop()      -> O(1)
+// top()      -> O(1)
+// getMin()   -> O(1)
+//
+// Space Complexity :
+// O(N) where N is the number of elements in the stack
+// (We use two stacks: one for values, one for tracking minimums)
+//
+// Did this code successfully run on Leetcode :
+// Yes
+//
+// Any problem you faced while coding this :
+// No major issues. The key idea was to:
+// - Keep an extra stack to track the minimum at each level
+// - Always push the current minimum along with each value
+// - Update the min correctly after pop using the min stack
+
+
+// Your code here along with comments explaining your approach
+
+import java.util.Stack;
+
+class MinStack {
+
+    // Main stack to store all values
+    private Stack<Integer> mainst;
+
+    // Auxiliary stack to store the minimum value at each level
+    private Stack<Integer> minst;
+
+    // Variable to track current minimum
+    private int min;
+
+    public MinStack() {
+        this.mainst = new Stack<>();
+        this.minst = new Stack<>();
+
+        // Initialize min with maximum possible value
+        this.min = Integer.MAX_VALUE;
+
+        // Push initial min so that peek() is always safe
+        this.minst.push(this.min);
+    }
+
+    public void push(int val) {
+        // Update the current minimum
+        min = Math.min(min, val);
+
+        // Push value into main stack
+        mainst.push(val);
+
+        // Push the updated minimum into min stack
+        minst.push(min);
+    }
+
+    public void pop() {
+        // Pop from both stacks to keep them in sync
+        mainst.pop();
+        minst.pop();
+
+        // Update current min to the new top of min stack
+        min = minst.peek();
+    }
+
+    public int top() {
+        // Return the top of the main stack
+        return mainst.peek();
+    }
+
+    public int getMin() {
+        // Return the current minimum value
+        return min;
+    }
+}
+
+/**
+ * Your MinStack object will be instantiated and called as such:
+ * MinStack obj = new MinStack();
+ * obj.push(val);
+ * obj.pop();
+ * int param_3 = obj.top();
+ * int param_4 = obj.getMin();
+ */

MyHashSet.java

@@ -0,0 +1,83 @@
+// Time Complexity :
+// add(key)      -> Average: O(1), Worst: O(n) (when many keys land in same bucket)
+// remove(key)   -> Average: O(1), Worst: O(n)
+// contains(key) -> Average: O(1), Worst: O(n)
+// (n = number of elements in the bucket due to collisions)
+//
+// Space Complexity :
+// O(N + B) where N = total keys stored, B = number of buckets (1000)
+//
+// Did this code successfully run on Leetcode :
+// Yes
+//
+// Any problem you faced while coding this :
+// No major issues. The main thing to be careful about is:
+// - Initializing the LinkedList bucket only when needed (lazy init)
+// - Removing by value using Integer.valueOf(key) so it doesn't treat key as an index
+// - Handling negative keys safely using Math.floorMod
+
+
+// Your code here along with comments explaining your approach
+
+import java.util.LinkedList;
+
+class MyHashSet {
+    // Number of buckets (fixed size). More buckets => fewer collisions on average.
+    int parentbuckets;
+
+    // Array of buckets; each bucket is a LinkedList to handle collisions (separate chaining).
+    LinkedList<Integer>[] storage;
+
+    public MyHashSet() {
+        // Chosen bucket size (common for this LeetCode problem).
+        this.parentbuckets = 1000;
+
+        // Create an array of LinkedLists (buckets). Buckets are initialized lazily.
+        this.storage = new LinkedList[parentbuckets];
+    }
+
+    // Primary hash function: maps the key into a valid bucket index [0..parentbuckets-1]
+    // floorMod ensures negative keys also map correctly.
+    private int getPrimaryHash(int key) {
+        return Math.floorMod(key, parentbuckets);
+    }
+
+    public void add(int key) {
+        int index = getPrimaryHash(key);
+
+        // Lazy bucket creation (saves memory for unused buckets)
+        if (storage[index] == null) {
+            storage[index] = new LinkedList<>();
+        }
+
+        // Avoid duplicates: only add if it's not already present
+        if (!storage[index].contains(key)) {
+            storage[index].add(key);
+        }
+    }
+
+    public void remove(int key) {
+        int index = getPrimaryHash(key);
+
+        // If bucket exists, remove the key if present
+        if (storage[index] != null) {
+            // Integer.valueOf(key) removes the object, not by index
+            storage[index].remove(Integer.valueOf(key));
+        }
+    }
+
+    public boolean contains(int key) {
+        int index = getPrimaryHash(key);
+
+        // Key exists if bucket exists and it contains the key
+        return storage[index] != null && storage[index].contains(key);
+    }
+}
+
+/**
+ * Your MyHashSet object will be instantiated and called as such:
+ * MyHashSet obj = new MyHashSet();
+ * obj.add(key);
+ * obj.remove(key);
+ * boolean param_3 = obj.contains(key);
+ */