linkedlist removelast

Author: amejiarosario

src/linked-list/linkedlist.js

@@ -6,8 +6,8 @@ const Node = require('./node');
  */
 class LinkedList {
   constructor() {
-    this.head = null;
-    this.tail = null;
+    this.head;
+    this.tail;
     this.length = 0;
   }
 
@@ -54,6 +54,34 @@ class LinkedList {
     return this.addFirst(dataOrNode);
   }
 
+  /**
+   * O(n)
+   * @returns {*}
+   */
+  removeLast() {
+    const last = this.tail;
+
+    if(!last) { return; }
+
+    let beforeLast = this.head;
+    while(beforeLast.next && beforeLast.next.next) { beforeLast = beforeLast.next; }
+
+    if(beforeLast === this.head && !this.head.next) {
+      this.head = null;
+      this.tail = null;
+    } else {
+      beforeLast.next = null;
+      this.tail = beforeLast;
+    }
+    this.length --;
+
+    return last.data;
+  }
+
+  removeFirst() {
+
+  }
+
   // O(n)
   delete(data) {
     let n = this.head;

src/linked-list/linkedlist.spec.js

@@ -4,9 +4,12 @@ const LinkedList = require('./linkedlist');
 describe('LinkedList', function () {
   let list;
 
+  beforeEach(function () {
+    list = new LinkedList();
+  });
+
   describe('.addLast', function () {
     beforeEach(function () {
-      list = new LinkedList();
       list.addLast(1);
       list.addLast(2);
       list.addLast(3);
@@ -37,7 +40,6 @@ describe('LinkedList', function () {
 
   describe('.addFirst', function () {
     beforeEach(function () {
-      list = new LinkedList();
       list.addFirst(1);
       list.addFirst(2);
       list.addFirst(3);
@@ -71,6 +73,32 @@ describe('LinkedList', function () {
     });
   });
 
+  describe('.removeLast', function () {
+    it('should handle empty', function () {
+      expect(list.removeLast()).to.equal(undefined);
+    });
+
+    it('should remove item', function () {
+      list.add(1);
+      expect(list.removeLast()).to.equal(1);
+    });
+
+    it('should remove multiple items', function () {
+      list.addLast(1);
+      list.addLast(2);
+
+      expect(list.removeLast()).to.equal(2);
+      expect(list.tail.data).to.equal(1);
+      expect(list.head.data).to.equal(1);
+      expect(list.size()).to.equal(1);
+
+      expect(list.removeLast()).to.equal(1);
+      expect(list.tail).to.equal(null);
+      expect(list.head).to.equal(null);
+      expect(list.size()).to.equal(0);
+    });
+  });
+
   describe('.delete', function () {
     beforeEach(function () {
       list = new LinkedList();