2.7 clean up

Author: amejiarosario

src/linked-list/linkedlist.js

@@ -16,7 +16,7 @@ class LinkedList {
    * @param dataOrNode
    * @returns {Node}
    */
-  addLast(dataOrNode){
+  addLast(dataOrNode, once = false){
     let node = getNode(dataOrNode);
     if(this.head) {
       this.tail.next = node;
@@ -27,7 +27,7 @@ class LinkedList {
     while(node) {
       this.tail = node;
       this.length++;
-      if(!node.next) { break; }
+      if(!node.next || once) { break; }
       node = node.next;
     }
     return node;

src/linked-list/loop-detection.js

@@ -0,0 +1,56 @@
+const LinkedList = require('./linkedlist');
+
+
+LinkedList.prototype.getLoop = loopDetection;
+
+/**
+ * O(n) / O(1) -
+ * @returns {*}
+ */
+function loopDetection() {
+  let slow = this.head;
+  let fast = this.head;
+
+  // first collision will happen k nodes before the beginning of the loop.
+  // k it also happen to be the distance from the head to the beginning of the loop
+  while(slow && fast.next) {
+    slow = slow.next;
+    fast = fast.next.next;
+    if(slow === fast) { break; }
+  }
+
+  // loop detected
+  // rewind slow and move both one at time.
+  // When they meet together is the beginning of the loop
+  if(slow === fast) {
+    for(slow = this.head; slow && fast; slow = slow.next, fast = fast.next) {
+      if(slow === fast) {
+        return slow;
+      }
+    }
+  }
+
+  // no loop detected
+  return false;
+
+}
+
+/**
+ * O(n) / O(n) - hashmap of addresses
+ * @returns {*}
+ */
+function hasLoop() {
+  var map = new Map();
+
+  for(let i = this.head; i; i = i.next) {
+    if(map.has(i)) {
+      return i;
+    } else {
+      map.set(i, 1);
+    }
+  }
+
+  return false;
+}
+
+module.exports = LinkedList;

src/linked-list/loop-detection.spec.js

@@ -0,0 +1,48 @@
+const expect = require('chai').expect;
+const LinkedList = require('./loop-detection');
+
+describe('LinkedList: loop detection', function () {
+  let list;
+
+  beforeEach(function () {
+    list = new LinkedList();
+  });
+
+  it('should return false when no loops are detected', function () {
+    list.addLast('a');
+    list.addLast('b');
+    list.addLast('c');
+    list.addLast('d');
+    list.addLast('e');
+
+    expect(list.getLoop()).to.equal(false);
+  });
+
+  it('should detect loop: case 1', function () {
+    list.addLast('a');
+    const b = list.addLast('b');
+    list.addLast(b, true);
+
+    expect(list.getLoop()).to.equal(b);
+  });
+
+  it('should detect loop: case 2', function () {
+    const a = list.addLast('a');
+    list.addLast('b');
+    list.addLast('c');
+    list.addLast(a, true);
+
+    expect(list.getLoop()).to.equal(a);
+  });
+
+  it('should detect loop: case 3', function () {
+    list.addLast('a');
+    list.addLast('b');
+    const c = list.addLast('c');
+    list.addLast('d');
+    list.addLast('e');
+    list.addLast(c, true);
+
+    expect(list.getLoop()).to.equal(c);
+  });
+});