add stack

Author: justanotherdev-in

Readme.md

@@ -30,3 +30,7 @@ This repository contains Data Structures implementation using Javascript.
 
 * [Doubly Linked List implementation](doubly-linked-list/doubly-linked-list.js)
 
+### Stack
+
+* [Stack implementation](stack/stack.js)
+

linked-list/linked-list.js

@@ -51,8 +51,10 @@ LinkedList.prototype.deleteAtIndex = function(index) {
         i++;
     }
 
+    const nodeToDelete = pre.next;
     pre.next = pre.next.next;
     this.size -= 1;
+    return nodeToDelete;
 }
 
 LinkedList.prototype.getNodeAtIndex = function(index) {
@@ -67,7 +69,7 @@ LinkedList.prototype.getNodeAtIndex = function(index) {
         i++;
     }
 
-    return pre.value;
+    return pre;
 }
 
 exports.LinkedList = LinkedList

stack/stack.js

@@ -0,0 +1,51 @@
+// Linked List
+// Pop / Push (add, remove) at one end in stack
+// Linked List 
+
+const { LinkedList } = require('../linked-list/linked-list');
+
+function Stack() {
+    this.stack = new LinkedList();
+}
+
+// Stack is empty -- isEmpty
+// Find element at top -- peek
+// Push -- push
+// Pop --- pop
+
+Stack.prototype.isEmpty = function() {
+    return this.stack.size === 0;
+}
+
+// Push and Pop at the same end
+// Linked List - we can access the first index in constant time 
+// Push 1 ---> 1
+// Push 2 ---> 2 --- 1
+// Push 3 ---> 3 --- 2 --- 1
+Stack.prototype.push = function(value) {
+    this.stack.addAtIndex(0, value);
+    // console.log(this.stack);
+}
+
+// Stack ---> 3 --- 2 --- 1
+// Pop ---> 2 --- 1
+// Pop ---> 1
+Stack.prototype.pop = function() {
+    if (this.isEmpty()) {
+        return null;
+    }
+
+    const node = this.stack.deleteAtIndex(0);
+    return node.value;
+}
+
+Stack.prototype.peek = function() {
+    if (this.isEmpty()) {
+        return null;
+    }
+
+    const node = this.stack.getNodeAtIndex(0);
+    return node.value;
+}
+
+exports.Stack = Stack;

stack/test-stack.js

@@ -0,0 +1,12 @@
+const { Stack } = require("./stack");
+
+const stack = new Stack();
+
+stack.push(1);
+console.log(stack.peek())
+stack.push(2);
+console.log(stack.peek())
+stack.push(3);
+console.log(stack.peek())
+console.log(stack.pop());
+console.log(stack.peek());