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Commit 4989a6a

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hanhdttrekhleb
authored andcommitted
Add LinkedList traversal and reverse implementations (trekhleb#194)
* Add LinkedList traverse function * Add LinkedList reverse traversal implementations * Update LinkedList traverse function * Update LinkedList reverse traversal and test cases * Update LinkedList traversal tests
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‎src/data-structures/linked-list/LinkedList.js‎

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@@ -207,4 +207,66 @@ export default class LinkedList {
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toString(callback) {
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return this.toArray().map(node => node.toString(callback)).toString();
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}
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/**
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* Traverse through all nodes of the list from head to tail
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* @param {*} callback
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* @return {LinkedListNode[]}
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*/
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traverse(callback = undefined) {
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if (typeof callback !== 'function') {
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throw new TypeError(`traverse method requires a callback function as an argument.\nArgument given: ${typeof callback}`);
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}
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let currentNode = this.head;
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const traversedNodes = [];
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while (currentNode) {
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traversedNodes.push(callback(currentNode.value));
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currentNode = currentNode.next;
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}
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return traversedNodes;
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}
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/**
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* The items in the list have been traversed in reverse order
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*/
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reverseTraversal(node, callback = undefined) {
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if (typeof callback !== 'function') {
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throw new TypeError(`reverseTraverse method requires a callback function as an argument.\nArgument given: ${typeof callback}`);
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}
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if (!node) return [];
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return this.reverseTraversal(node.next, callback).concat(callback(node.value));
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}
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/**
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* Reverse a singly linked list use to three variables
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* @returns {ReservedLinkedList}
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*/
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reverse() {
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let currNode = this.head;
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let prevNode = null;
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let nextNode = null;
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while (currNode) {
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// Store next node
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nextNode = currNode.next;
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// Change next node of the current
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currNode.next = prevNode;
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// Move forward prev and current nodes one step
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prevNode = currNode;
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currNode = nextNode;
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}
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// Reset head, tail
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this.tail = this.head;
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this.head = prevNode;
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return this;
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}
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}

‎src/data-structures/linked-list/README.md‎

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@@ -110,24 +110,24 @@ Traverse(head)
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Pre: head is the head node in the list
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Post: the items in the list have been traversed
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n ← head
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while n = 0
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while n != ø
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yield n.value
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n ← n.next
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end while
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end Traverse
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```
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### Traverse in Reverse
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```text
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ReverseTraversal(head, tail)
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Pre: head and tail belong to the same list
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Post: the items in the list have been traversed in reverse order
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if tail = ø
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if tail != ø
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curr ← tail
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while curr = head
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while curr != head
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prev ← head
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while prev.next = curr
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while prev.next != curr
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prev ← prev.next
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end while
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yield curr.value

‎src/data-structures/linked-list/__test__/LinkedList.test.js‎

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@@ -217,4 +217,41 @@ describe('LinkedList', () => {
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expect(node.value.customValue).toBe('test2');
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expect(linkedList.find({ value: 2, customValue: 'test5' })).toBeNull();
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});
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it('should traverse through all nodes of the list from head to tail with callback', () => {
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const linkedList = new LinkedList();
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linkedList
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.append(1)
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.append(2)
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.append(3);
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expect(linkedList.traverse(value => value * 2)).toEqual([2, 4, 6]);
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expect(() => linkedList.traverse()).toThrow();
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});
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it('should reverse traversal the linked list with callback', () => {
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const linkedList = new LinkedList();
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linkedList
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.append(1)
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.append(2)
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.append(3);
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expect(linkedList.toString()).toBe('1,2,3');
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expect(linkedList.reverseTraversal(linkedList.head, value => value * 2)).toEqual([6, 4, 2]);
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expect(() => linkedList.reverseTraversal(linkedList.head)).toThrow();
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});
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it('should reverse the singly linked list', () => {
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const linkedList = new LinkedList();
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linkedList
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.append(1)
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.append(2)
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.append(3);
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expect(linkedList.toString()).toBe('1,2,3');
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expect(linkedList.reverse().toString()).toBe('3,2,1');
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});
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});

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