chore(Javascript): add doubly linked-list (#299)

algorithms/JavaScript/README.md

@@ -5,6 +5,8 @@
 
 ## Linked Lists
 1. [Singly](lsrc/inked_lists/singly.js)
+1. [Doubly](lsrc/inked_lists/doubly.js)
+
  
 ## Searching
 1. [Binary Search Recursive](src/searching/binary-search-recursive.js)

algorithms/JavaScript/src/linked-lists/doubly.js

@@ -0,0 +1,159 @@
+
+function DoubleLinkedList() {
+  const Node = function(element) {
+    this.element = element;
+    this.next = null;
+    this.prev = null;
+  };
+
+  let length = 0;
+  const head = new Node('head');
+  let tail = head;
+
+  // Add new element
+  this.append = function(element) {
+    const node = new Node(element);
+
+    node.prev = tail;
+    tail.next = node;
+    tail = node;
+
+
+    length++;
+  };
+
+  // Add element
+  this.insert = function(position, element) {
+    // Check of out-of-bound values
+    if (position >= 0 && position <= length) {
+      const node = new Node(element);
+      let current = head;
+      let index = 0;
+
+      while (index < position) {
+        current = current.next;
+        index++;
+      }
+      node.next = current.next;
+      if (node.next !== null) {
+        node.next.prev = node;
+      }
+      node.prev = current;
+      current.next = node;
+
+      length++;
+      return true;
+    } else {
+      return null;
+    }
+  };
+
+  // Remove element at any position
+  this.removeAt = function(position) {
+    // look for out-of-bounds value
+
+    if (position > -1 && position < length) {
+      let current = head;
+      let index = 0;
+
+      while (index < position) {
+        current = current.next;
+        index++;
+      }
+      if (current.next.next !== null) {
+        current.next.next.prev = current;
+      }
+
+      current.next = current.next.next;
+
+      length--;
+      return current.element;
+    } else {
+      return null;
+    }
+  };
+
+  // Get the indexOf item
+  this.indexOf = function(elm) {
+    let current = head;
+    let index = -1;
+
+    // If element found then return its position
+    while (current.next) {
+      if (elm === current.next.element) {
+        return ++index;
+      }
+
+      index++;
+      current = current.next;
+    }
+
+    // Else return -1
+    return -1;
+  };
+
+  // Delete an item from the list
+  this.delete = (elm) => {
+    return this.removeAt(this.indexOf(elm));
+  };
+
+  this.toString = function() {
+    let current = head.next;
+    let string = '';
+
+    while (current) {
+      string += current.element + ' ';
+      current = current.next;
+    }
+
+    return string;
+  };
+
+  // Convert list to array
+  this.toArray = function() {
+    const arr = [];
+    let current = head.next;
+
+    while (current) {
+      arr.push(current.element);
+      current = current.next;
+    }
+
+    return arr;
+  };
+
+  // Check if list is empty
+  this.isEmpty = function() {
+    return length === 0;
+  };
+
+  // Get the size of the list
+  this.size = function() {
+    return length;
+  };
+
+  // Get the head
+  this.getHead = function() {
+    return head.next;
+  };
+
+  // Get the tail
+  this.getTail = function() {
+    return tail;
+  };
+}
+
+
+const newDoubleLinkedList = new DoubleLinkedList();
+newDoubleLinkedList.append(1);
+newDoubleLinkedList.append(5);
+newDoubleLinkedList.append(3);
+newDoubleLinkedList.append(20);
+newDoubleLinkedList.insert(1, 9);
+newDoubleLinkedList.removeAt(2);
+
+console.log(newDoubleLinkedList.toArray());
+console.log(newDoubleLinkedList.toString());
+
+newDoubleLinkedList.delete(20);
+console.log('After delete 20: '+newDoubleLinkedList.toString());