Implemented Hashmap and Queue using stacks

design-hashmap.java

@@ -0,0 +1,34 @@
+// Time Complexity :O(1)
+// Space Complexity :O(n)
+// Did this code successfully run on Leetcode :Yes
+// Any problem you faced while coding this :No
+
+import java.util.Arrays;
+class MyHashMap {
+
+    int[] hashstorage = new int[1000001];
+
+    public MyHashMap() {
+        Arrays.fill(hashstorage, -1);
+    }
+
+    public void put(int key, int value) {
+        hashstorage[key] = value;
+    }
+
+    public int get(int key) {
+        return hashstorage[key];
+    }
+
+    public void remove(int key) {
+        hashstorage[key]=-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);
+ */

implement-queue-using-stacks.java

@@ -0,0 +1,45 @@
+// Time Complexity : O(1)
+// Space Complexity : O(n)
+// Did this code successfully run on Leetcode : Yes
+// Any problem you faced while coding this :No
+
+import java.util.Stack;
+
+class MyQueue {
+   Stack<Integer> in = new Stack<>();
+   Stack<Integer> out = new Stack<>();
+    public MyQueue() {
+
+    }
+
+    public void push(int x) {
+        in.push(x);
+    }
+
+    public int pop() {
+        peek();
+        return out.pop();
+    }
+
+    public int peek() {
+        if(out.isEmpty()){
+            while(!in.isEmpty()){
+                out.push(in.pop());
+            }
+        }
+        return out.peek();
+    }
+
+    public boolean empty() {
+        return out.isEmpty() && in.isEmpty();
+    }
+}
+
+/**
+ * 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();
+ */