3.2 after taking a peek on the book, better solution

Author: amejiarosario

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

@@ -9,6 +9,7 @@ class MinStack {
   constructor() {
     this.head = null;
     this.minNode = null;
+    this.minimums = [];
   }
 
   /**
@@ -22,12 +23,14 @@ class MinStack {
       node.next = this.head;
     } else {
       this.minNode = node;
+      this.minimums.push(node);
     }
 
     this.head = node;
 
     if(this.minNode.data > node.data) {
       this.minNode = node;
+      this.minimums.push(node);
     }
   }
 
@@ -37,11 +40,21 @@ class MinStack {
    */
   pop() {
     const out = this.head;
+
+    if(!out) { return; }
+
     this.head = this.head.next;
+
+    if(out === this.minNode) {
+      this.minimums.pop();
+      this.minNode = this.minimums[this.minimums.length - 1];
+    }
+
     return out.data;
   }
 
   min() {
+    if(!this.minNode) { return; }
     return this.minNode.data;
   }
 }

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

@@ -22,6 +22,10 @@ describe('Stacks: MinStack', function () {
   });
 
   describe('.pop', function () {
+    it('should handle empty pops', function () {
+      expect(minstack.pop()).to.equal(undefined);
+    });
+
     it('should take the last element from the list', function () {
       minstack.push(1);
       expect(minstack.pop()).to.equal(1);
@@ -33,9 +37,20 @@ describe('Stacks: MinStack', function () {
       expect(minstack.pop()).to.equal(2);
       expect(minstack.pop()).to.equal(1);
     });
+
+    it('should remove all and beyond gracefully', function () {
+      minstack.push(1);
+      minstack.pop();
+      expect(minstack.pop()).to.equal(undefined);
+    });
   });
 
   describe('.min', function () {
+
+    it('should handle empty min', function () {
+      expect(minstack.min()).to.equal(undefined);
+    });
+
     it('should keep track of min', function () {
       minstack.push(1);
       expect(minstack.min()).to.equal(1);
@@ -55,5 +70,12 @@ describe('Stacks: MinStack', function () {
       minstack.pop(); // 1
       expect(minstack.min()).to.equal(10);
     });
+
+    it('should remove all and beyond gracefully', function () {
+      minstack.push(1);
+      minstack.pop();
+      minstack.pop();
+      expect(minstack.min()).to.equal(undefined);
+    });
   });
 });