Pre Course 1 Completed

Exercise_1.js

@@ -1,35 +1,53 @@
+// Time Complexity : push, pop, peek, isEmpty O(1)
+// Space Complexity : O(1) since we not creating any data structure in user facing functions.
+// Did this code successfully run on Leetcode : No
+// Any problem you faced while coding this : NO
+
 class Stack {
-  //Please read sample.java file before starting.
-  //Kindly include Time and Space complexity at top of each file
-​
-    constructor() {
-        //Initialize your constructor
-        this.MAX = 1000;
-        this.top = -1;
-        this.a = new Array(this.MAX);
+  //  Please read sample.java file before starting.
+  //  Kindly include Time and Space complexity at top of each file
+  constructor() {
+    //Initialize your constructor
+    this.MAX = 10;
+    this.top = -1; // Index of top element
+    this.a = new Array(this.MAX);
+  }
+
+  isEmpty() {
+    //Write your code here
+    return this.top === -1;
+  }
+
+  push(x) {
+    this.top += 1;
+    this.a[this.top] = x;
+  }
+
+  pop() {
+    //If empty return 0 and print " Stack Underflow"
+    if (this.isEmpty()) {
+      return 0;
     }
-​
-    function isEmpty() {
-        //Write your code here
-    }
-​
-    function push(x) {
-        //Check for stack Overflow
-        //Write your code here
-    }
-​
-    function pop() {
-        //If empty return 0 and print " Stack Underflow"
-        //Write your code here
-    }
-​
-    function peek() {
-       //Write your code here
+    let value = this.a[this.top];
+    this.a[this.top] = null;
+    this.top -= 1;
+    return value;
+  }
+
+  peek() {
+    //Write your code here
+    if (this.isEmpty()) {
+      return -1;
     }
+    this.a[this.top];
+  }
 }
-​
-let s = new Stack();
-s.push(10);
-s.push(20);
-s.push(30);
-console.log(s.pop() + " Popped from stack");
+
+test("Scenario #1:", () => {
+  let obj = new Stack();
+  obj.push(10);
+  obj.push(20);
+  obj.push(30);
+
+  expect(obj.pop()).toStrictEqual(30);
+});