Completed Design-2

HashMap.java

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+
+//Hashmap implementation with array of type Node (linked list)
+
+
+
+// Time Complexity :  time complexity of O(1) , it doesn't traverse more than 100 items per operation
+// Space Complexity : allocating O(n) node spaces
+// Did this code successfully run on Leetcode : yes
+// Any problem you faced while coding this : wiritng getPrev and handling null pointer exception is something took time for me.
+
+class MyHashMap {
+
+    Node[] storage;
+    int buckets;
+
+    class Node{
+        int key;
+        int value;
+        Node next;
+
+        public Node(int key , int value){
+            this.key = key;
+            this.value = value;
+            this.next = null;
+        }
+    }
+
+    public MyHashMap() {
+
+    this.buckets = 10000;
+    storage = new Node[buckets];
+
+
+    }
+    public int getHash(int key){
+        return key % buckets;
+
+    }
+
+    public Node getPrev(Node head, int key) {
+        Node prev = null;
+        Node curr = head;
+        while(curr != null && curr.key != key ){
+            prev = curr;
+            curr = curr.next;
+        }
+        return prev;
+
+    }
+
+
+
+
+    public void put(int key, int value) {
+        int index = getHash(key);
+        if(storage[index] == null){
+            Node firstNode = new Node(-1,-1);
+            storage[index] = firstNode;
+            storage[index].next = new Node(key,value);
+            return;
+        }
+           Node prev = getPrev(storage[index], key);
+        if(prev.next == null){ 
+            prev.next = new Node(key, value);
+        }else{ 
+            prev.next.value = value;
+        }
+
+
+    }
+
+    public int get(int key) {
+        int index = getHash(key);
+        if(storage[index] == null) return -1;
+        Node prev = getPrev(storage[index], key);
+        if(prev.next == null) return -1;
+        return prev.next.value;
+
+    }
+
+    public void remove(int key) {
+         int index = getHash(key);
+        if(storage[index] == null ){
+        return;
+        }
+        if( getPrev(storage[index], key).next == null ){
+            return ;
+        } else {
+        getPrev(storage[index], key).next = getPrev(storage[index], key).next.next;
+        }
+    }
+}
+
+/**
+ * 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);
+ */

Queue.java

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+//Problem 1: (https://leetcode.com/problems/implement-queue-using-stacks/)
+
+// Implement Queue using 2 Stacks
+// 
+
+// Time Complexity : Amortized O(1) time complexity for pop and peek
+// Space Complexity : O(n)
+// Did this code successfully run on Leetcode : yes
+// Any problem you faced while coding this : checking if outStack and is empty and instack is not empty condition took some time for me
+// followed the same approach as in class
+
+class MyQueue {
+        Stack<Integer> inStack ;
+          Stack<Integer> outStack;
+
+
+    public MyQueue() {
+
+    inStack = new Stack<Integer>();
+      outStack = new Stack<Integer>();
+
+    }
+
+    public void push(int x) {
+        inStack.push(x);
+    }
+
+    public int pop() {
+         if (outStack.isEmpty()) {
+        while (!inStack.isEmpty()) {
+            outStack.push(inStack.pop());
+        }
+    }
+
+    if (outStack.isEmpty()) {
+        return -1;   // queue is empty
+    }
+
+    return outStack.pop();
+
+    }
+
+    public int peek() {
+      if (outStack.isEmpty()) {
+        while (!inStack.isEmpty()) {
+            outStack.push(inStack.pop());
+        }
+    }
+
+    if (outStack.isEmpty()) {
+        return -1;   // queue is empty
+    }
+
+    return outStack.peek();
+
+    }
+
+    public boolean empty() {
+        if(inStack.isEmpty() && outStack.isEmpty()){
+            return true;
+        }
+        return false;
+
+    }
+}
+
+/**
+ * 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();
+ */