➕ chapter-2: Delete middle node of SLL (careercup#5)

*  find middle node of a Singly Linked List

*  find middle node of a Singly Linked List

*  find middle node of a Singly Linked List

* add find-middle node tests

* Delete middle Node of Linked List

* correct2-3-Delete Middle Node

*  add solution for access to the head  / or access to middle-node

* 2-2: rturn Kth to Last

* add for loop for craating new node in  beforeEach for tests

* 2-8: Detection Loop in SLL

Author: Raziyehbazargan

README.md

@@ -4,7 +4,7 @@
 
 ## Question List:
 
-#### Chapter 1 
+#### Chapter 1
 - [x] 1.1 - [Is Unique](lib/data-structures/chapter-1/1_1.js)
 - [x] 1.2 - [Check Permutation](lib/data-structures/chapter-1/1_2.js)
 - [x] 1.3 - [URLify](lib/data-structures/chapter-1/1_3.js)
@@ -13,7 +13,13 @@
 - [x] 1.6 - [String Compression](lib/data-structures/chapter-1/1_6.js)
 - [x] 1.7 - [Rotate Matrix](lib/data-structures/chapter-1/1_7.js)
 - [x] 1.8 - [Zero Matrix](lib/data-structures/chapter-1/1_8.js)
-- [ ] 1.9 - String Rotation 
+- [ ] 1.9 - String Rotation
+
+#### Chapter 2
+- [x] 2.2 - [Return Kth to Last](lib/data-structures/chapter-2/2_2.js)
+- [x] 2.3 - [Delete Middle Node](lib/data-structures/chapter-2/2_3.js)
+- [x] 2.8 - [Detection Loop](lib/data-structures/chapter-2/2_8.js)
+
 
 #### Chapter 3
 - [ ] 3.1 - Three in One
@@ -38,7 +44,7 @@ npm install
 npm test
 ```
 
-If you just want to lint  
+If you just want to lint
 ```bash
 npm run lint
 ```

lib/data-structures/chapter-2/2_2.js

@@ -0,0 +1,19 @@
+var SLL = require('./helper.js');
+
+  SLL.prototype.nthToLast = function(head, k) {
+    var p1 = head,
+        p2 = head;
+
+    for (var i = 0; i < k; i++) {
+      if (p1 === null) {
+        return null;
+      }
+      p1 = p1.next;
+    }
+
+    while(p1 !== null) {
+      p1 = p1.next;
+      p2 = p2.next;
+    }
+    return p2;
+  };

lib/data-structures/chapter-2/2_3.js

@@ -0,0 +1,57 @@
+var SLL = require('./helper.js');
+
+  function Node(data, next) {
+    this.data = data,
+    this.next = next;
+  }
+
+  SLL.prototype.addNode = function(data, next) {
+    var node = new Node(data, next),
+        current = this.head;
+
+    if (this.head === null) {
+      this.head = node;
+      this.length++;
+      return;
+    }
+    while (current.next) {
+      current = current.next;
+    }
+    current.next = node;
+    this.length++;
+  };
+
+  //solution for delete middle node with access to the head of LinkedList
+  SLL.prototype.findMiddleAndRemove = function(head) {
+    ( head === null || head.next === null ) ? null : head;
+
+    var slowPointer = head,
+        fastPointer = head,
+        previous = null;
+
+    while(fastPointer.next !== null && fastPointer.next.next !== null) {
+      fastPointer = fastPointer.next.next;
+      previous = slowPointer;
+      slowPointer = slowPointer.next;
+    }
+
+    previous.next = slowPointer.next;
+    this.length--;
+  };
+
+  //solution for delete middle node with access to the node ( middle node ) not the head of LinkedList
+  SLL.prototype.removeMiddleNode = function(currentNode) {
+    if ( currentNode === null || currentNode.next === null) {
+      return false;
+    }
+    //copy next node data to current node
+    var nextNode = currentNode.next;
+    currentNode.data = nextNode.data;
+    currentNode.next = nextNode.next;
+
+    //remove next node
+    currentNode.next = nextNode.next;
+    this.length--;
+  };
+
+  //return MyLinkedList;

lib/data-structures/chapter-2/2_8.js

@@ -0,0 +1,28 @@
+var SLL = require('./helper.js');
+
+  SLL.prototype.findBeginning = function(head) {
+    var slow = head,
+        fast = head;
+
+    //find meeting point
+    while (fast !== null && fast.next !== null) {
+      slow = slow.next;
+      fast = fast.next.next;
+      if (slow === fast) {
+        break;
+      }
+    }
+    
+    // no loop
+    if (fast === null || fast.next === null) {
+      return null;
+    }
+
+    // move slow to head. keep fast at meeting point. if they move at the same pace, they must meet at the loop start.
+    slow = head;
+    while (slow !== fast) {
+      slow = slow.next;
+      fast = fast.next;
+    }
+    return fast;
+  };

lib/data-structures/chapter-2/helper.js

@@ -0,0 +1,9 @@
+module.exports = MyLinkedList = (function(){
+
+  function MyLinkedList() {
+     this.head = null;
+     this.length = 0;
+  }
+  
+  return MyLinkedList;
+})();

test/data-structures/chapter-2/2_2_Spec.js

@@ -0,0 +1,23 @@
+require('../../test_helper');
+
+describe('2.2 #nthToLast', function () {
+  describe('return Kth element to last', function () {
+    var sll;
+    beforeEach(function() {
+      sll = new MyLinkedList();
+      for(var i=1; i < 6; i++) {
+        sll.addNode( i + 'Node', null);
+      }
+    });
+
+    afterEach(function() {
+      sll = null;
+    });
+
+    it('should return Kth element to last', function () {
+      var kthNode = sll.nthToLast(sll.head, 3);
+      expect(kthNode).to.not.be.null;
+      expect(kthNode).to.have.property('data').and.be.equal('3Node');
+    });
+  });
+});

test/data-structures/chapter-2/2_3_Spec.js

@@ -0,0 +1,32 @@
+require('../../test_helper');
+
+describe('2.3 #FindMiddle', function () {
+  describe('return middle Node', function () {
+    var sll;
+    beforeEach(function() {
+      sll = new MyLinkedList();
+      for(var i=1; i < 6; i++) {
+        sll.addNode( i + 'Node', null);
+      }
+    });
+
+    afterEach(function() {
+      sll = null;
+    });
+
+    it('should return correct length of LinkedList', function () {
+      expect(sll).length.to.be(5);
+    });
+
+    it('should remove the middle node with aceess to the head of SLL', function () {
+      sll.findMiddleAndRemove(sll.head);
+      expect(sll).length.to.be(4);
+    });
+
+    it('should remove the middle node with access to the middle_node not head', function () {
+      sll.removeMiddleNode(sll.head.next.next);
+      expect(sll).length.to.be(4);
+    });
+
+  });
+});

test/data-structures/chapter-2/2_8_Spec.js

@@ -0,0 +1,25 @@
+require('../../test_helper');
+
+describe('2.8 #findBeginning', function () {
+  describe('find loop in Singly Linkedlist', function () {
+    var sll;
+    beforeEach(function() {
+      sll = new MyLinkedList();
+      for(var i=1; i < 6; i++) {
+        sll.addNode( i + 'Node', null);
+      }
+      //create loop in linkedlist 
+      sll.addNode('6Node', sll.head.next.next.next);
+    });
+
+    afterEach(function() {
+      sll = null;
+    });
+
+    it('should return loop start (node) in SLL', function () {
+      var loopPoint = sll.findBeginning(sll.head);
+      expect(loopPoint).not.be.null;
+      expect(loopPoint).to.have.property('data').and.be.equal('4Node');
+    });
+  });
+});