Complete Design-2 assignment

ImplementHashMap.java

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+//Approach: Similar to HashSet implementation try using double-hashing method
+// to handle collisions
+
+// Time Complexity: O(1)
+// Space Complexity: O(1)
+
+class MyHashMap {
+
+    int[][] arr;
+    int buckets;
+    int bucketItems;
+
+    public MyHashMap() {
+        buckets = 1000;
+        bucketItems = 1000;
+        arr = new int[buckets][];
+    }
+
+    public int getPrimaryHash(int key)
+    {
+        return key % buckets;
+    }
+
+    public int getSecondaryHash(int key)
+    {
+        return key / bucketItems;
+    }
+
+    public void put(int key, int value) {
+        var firstIndex = getPrimaryHash(key);
+        var secondIndex = getSecondaryHash(key);
+        if (arr[firstIndex] == null)
+        {
+            if (firstIndex == 0)
+            {
+                arr[firstIndex] = new int[bucketItems + 1];
+            }
+            else
+            {
+                arr[firstIndex] = new int[bucketItems];
+            }
+        }
+        if (value == 0)
+        {
+            arr[firstIndex][secondIndex] = value - 2;
+        }
+        else
+        {
+            arr[firstIndex][secondIndex] = value;
+        }
+    }
+
+    public int get(int key) {
+        var firstIndex = getPrimaryHash(key);
+        var secondIndex = getSecondaryHash(key);
+
+        if (arr[firstIndex] == null || arr[firstIndex][secondIndex] == 0)
+        {
+            return -1;
+        }
+        if (arr[firstIndex][secondIndex] == -2)
+        {
+            return 0;
+        }
+        return arr[firstIndex][secondIndex];
+    }
+
+    public void remove(int key) {
+        var firstIndex = getPrimaryHash(key);
+        var secondIndex = getSecondaryHash(key);
+        if (arr[firstIndex] == null || arr[firstIndex][secondIndex] == -1) return;
+        arr[firstIndex][secondIndex] = -1;
+    }
+}
+/**
+ * Your MyHashMap object will be instantiated and called as such:
+ * MyHashMap obj = new MyHashMap();
+ * obj.put(key,value);
+ * int param_2 = obj.get(key);
+ * obj.remove(key);
+ */

ImplementQueueUsingStacks.java

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+//Approach: The idea is to hold elements in one stack, until a pop() or peek() happens and copy the elements from first stack to another and then pop() or peek()
+
+// Time Complexity for Pop() and Peek() is O(n) (as linear traversal is involved)
+// Time Complexity for Push() and empty() is O(1)
+
+// Space Complexity: O(n), as we have to maintain another stack to temporarily hold elements for pop() and peek() operations
+
+class MyQueue {
+
+    Stack<Integer> firstStack;
+    Stack<Integer> secondStack;
+
+    public MyQueue() {
+        firstStack = new Stack<>();
+        secondStack = new Stack<>();
+    }
+
+    public void push(int x) {
+        firstStack.push(x);
+    }
+
+    public int pop() {
+        peek();
+        return secondStack.pop();
+    }
+
+    public int peek() {
+        if(secondStack.size() == 0){
+            while(firstStack.size() != 0)
+            {
+                secondStack.push(firstStack.pop());
+            }
+        }
+
+        return secondStack.peek();
+    }
+
+    public boolean empty() {
+        return firstStack.size() == 0 && secondStack.size() == 0;
+    }
+}
+
+/**
+ * Your MyQueue object will be instantiated and called as such:
+ * MyQueue obj = new MyQueue();
+ * obj.push(x);
+ * int param_2 = obj.pop();
+ * int param_3 = obj.peek();
+ * boolean param_4 = obj.empty();
+ */