3.2 my solution failing on removing multiple min

Author: amejiarosario

src/stacks-and-queues/min-stack.js

@@ -0,0 +1,49 @@
+class Node {
+  constructor(data) {
+    this.data = data;
+    this.next = null;
+  }
+}
+
+class MinStack {
+  constructor() {
+    this.head = null;
+    this.minNode = null;
+  }
+
+  /**
+   * AddFirst O(1)
+   * @param data
+   */
+  push(data) {
+    const node = new Node(data);
+
+    if(this.head) {
+      node.next = this.head;
+    } else {
+      this.minNode = node;
+    }
+
+    this.head = node;
+
+    if(this.minNode.data > node.data) {
+      this.minNode = node;
+    }
+  }
+
+  /**
+   * RemoveFirst
+   * @returns {*}
+   */
+  pop() {
+    const out = this.head;
+    this.head = this.head.next;
+    return out.data;
+  }
+
+  min() {
+    return this.minNode.data;
+  }
+}
+
+module.exports = MinStack;

src/stacks-and-queues/min-stack.spec.js

@@ -0,0 +1,59 @@
+const expect = require('chai').expect;
+const MinStack = require('./min-stack');
+
+describe('Stacks: MinStack', function () {
+  var minstack;
+
+  beforeEach(function () {
+    minstack = new MinStack();
+  });
+
+  describe('.push', function () {
+    it('should add an element to stack', function () {
+      minstack.push(1);
+      expect(minstack.head.data).to.equal(1);
+    });
+
+    it('should add multiple elements to stack', function () {
+      minstack.push(1);
+      minstack.push(2);
+      expect(minstack.head.data).to.equal(2);
+    });
+  });
+
+  describe('.pop', function () {
+    it('should take the last element from the list', function () {
+      minstack.push(1);
+      expect(minstack.pop()).to.equal(1);
+    });
+
+    it('should remove element FIFO', function () {
+      minstack.push(1);
+      minstack.push(2);
+      expect(minstack.pop()).to.equal(2);
+      expect(minstack.pop()).to.equal(1);
+    });
+  });
+
+  describe('.min', function () {
+    it('should keep track of min', function () {
+      minstack.push(1);
+      expect(minstack.min()).to.equal(1);
+    });
+
+    it('should return min among other nodes', function () {
+      minstack.push(10);
+      minstack.push(15);
+      expect(minstack.min()).to.equal(10);
+      minstack.push(1);
+      expect(minstack.min()).to.equal(1);
+    });
+
+    it('should return 2nd min if the min is removed', function () {
+      minstack.push(10);
+      minstack.push(1);
+      minstack.pop(); // 1
+      expect(minstack.min()).to.equal(10);
+    });
+  });
+});