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Solve problem: Longest Palindrome & Linked List Cycle II
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‎README.MD

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@@ -4,25 +4,27 @@ Solving problems with LeetCode
44

55
## Problems
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| Title | Solution | Difficulty |
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|--------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------|------------|
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| [Contains Duplicate](https://leetcode.com/problems/contains-duplicate) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/containsDuplicate/index.js) | Easy |
10-
| [Missing Number](https://leetcode.com/problems/missing-number) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/tree/main/solutions/missingNumber/index.js) | Easy |
11-
| [Find All Numbers Disappeared in an Array](https://leetcode.com/problems/find-all-numbers-disappeared-in-an-array) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/findDisappearedNumbers/index.js) | Easy |
12-
| [Single Number](https://leetcode.com/problems/single-number) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/singleNumber/index.js) | Easy |
13-
| [Climbing Stairs](https://leetcode.com/problems/climbing-stairs) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/climbStairs/index.js) | Easy |
14-
| [Best Time to Buy and Sell Stock](https://leetcode.com/problems/best-time-to-buy-and-sell-stock) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/maxProfit/index.js) | Easy |
15-
| [Range Sum Query - Immutable](https://leetcode.com/problems/range-sum-query-immutable) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/sumRange/index.js) | Easy |
16-
| [Counting Bits](https://leetcode.com/problems/counting-bits) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/countBits/index.js) | Easy |
17-
| [Linked List Cycle](https://leetcode.com/problems/linked-list-cycle) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/hasCycle/index.js) | Easy |
18-
| [Middle of the Linked List](https://leetcode.com/problems/middle-of-the-linked-list) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/middleNode/index.js) | Easy |
19-
| [Reverse Linked List](https://leetcode.com/problems/reverse-linked-list) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/reverseList/index.js) | Easy |
20-
| [Palindrome Linked List](https://leetcode.com/problems/palindrome-linked-list) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/isPalindrome/index.js) | Easy |
21-
| [Remove Linked List Elements](https://leetcode.com/problems/remove-linked-list-elements) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/removeElements/index.js) | Easy |
22-
| [Two Sum](https://leetcode.com/problems/two-sum) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/twoSum/index.js) | Easy |
23-
| [Majority Element](https://leetcode.com/problems/majority-element) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/majorityElement/index.js) | Easy |
24-
| [Running Sum of 1d Array](https://leetcode.com/problems/running-sum-of-1d-array/) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/runningSum/index.js) | Easy |
25-
| [Find Pivot Index](https://leetcode.com/problems/find-pivot-index/) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/pivotIndex/index.js) | Easy |
26-
| [Is Subsequence](https://leetcode.com/problems/is-subsequence/) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/isSubsequence/isSubsequence.js) | Easy |
27-
| [Isomorphic Strings](https://leetcode.com/problems/isomorphic-strings/) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/isIsomorphic/isIsomorphic.js) | Easy |
28-
| [Merge Two Sorted Lists](https://leetcode.com/problems/merge-two-sorted-lists/) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/mergeTwoLists/mergeTwoLists.js) | Easy |
7+
| Title | Solution | Difficulty |
8+
|--------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------|------------|
9+
| [Contains Duplicate](https://leetcode.com/problems/contains-duplicate) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/containsDuplicate/index.js) | Easy |
10+
| [Missing Number](https://leetcode.com/problems/missing-number) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/tree/main/solutions/missingNumber/index.js) | Easy |
11+
| [Find All Numbers Disappeared in an Array](https://leetcode.com/problems/find-all-numbers-disappeared-in-an-array) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/findDisappearedNumbers/index.js) | Easy |
12+
| [Single Number](https://leetcode.com/problems/single-number) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/singleNumber/index.js) | Easy |
13+
| [Climbing Stairs](https://leetcode.com/problems/climbing-stairs) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/climbStairs/index.js) | Easy |
14+
| [Best Time to Buy and Sell Stock](https://leetcode.com/problems/best-time-to-buy-and-sell-stock) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/maxProfit/index.js) | Easy |
15+
| [Range Sum Query - Immutable](https://leetcode.com/problems/range-sum-query-immutable) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/sumRange/index.js) | Easy |
16+
| [Counting Bits](https://leetcode.com/problems/counting-bits) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/countBits/index.js) | Easy |
17+
| [Linked List Cycle](https://leetcode.com/problems/linked-list-cycle) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/hasCycle/index.js) | Easy |
18+
| [Middle of the Linked List](https://leetcode.com/problems/middle-of-the-linked-list) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/middleNode/index.js) | Easy |
19+
| [Reverse Linked List](https://leetcode.com/problems/reverse-linked-list) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/reverseList/index.js) | Easy |
20+
| [Palindrome Linked List](https://leetcode.com/problems/palindrome-linked-list) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/isPalindrome/index.js) | Easy |
21+
| [Remove Linked List Elements](https://leetcode.com/problems/remove-linked-list-elements) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/removeElements/index.js) | Easy |
22+
| [Two Sum](https://leetcode.com/problems/two-sum) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/twoSum/index.js) | Easy |
23+
| [Majority Element](https://leetcode.com/problems/majority-element) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/majorityElement/index.js) | Easy |
24+
| [Running Sum of 1d Array](https://leetcode.com/problems/running-sum-of-1d-array/) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/runningSum/index.js) | Easy |
25+
| [Find Pivot Index](https://leetcode.com/problems/find-pivot-index/) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/pivotIndex/index.js) | Easy |
26+
| [Is Subsequence](https://leetcode.com/problems/is-subsequence/) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/isSubsequence/isSubsequence.js) | Easy |
27+
| [Isomorphic Strings](https://leetcode.com/problems/isomorphic-strings/) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/isIsomorphic/isIsomorphic.js) | Easy |
28+
| [Merge Two Sorted Lists](https://leetcode.com/problems/merge-two-sorted-lists/) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/mergeTwoLists/mergeTwoLists.js) | Easy |
29+
| [Longest Palindrome](https://leetcode.com/problems/longest-palindrome/) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/longestPalindrome/longestPalindrome.js) | Easy |
30+
| [Linked List Cycle II](https://leetcode.com/problems/linked-list-cycle-ii/description/) | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/detectCycle/detectCycle.js) | Medium |

‎helpers/createLinkedListFromArray.js

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const ListNode = require('./listNode');
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/**
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* Creates a linked list from an array of values.
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*
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* @param {Array<number>} arr - The array of values to create the linked list from.
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* @returns {ListNode | null} The head node of the linked list, or null if the input array is empty.
8+
*/
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function createLinkedListFromArray(arr) {
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if (!arr || arr.length === 0) {
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return null;
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}
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let head = {
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val: arr[0],
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next: null,
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};
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let head = new ListNode(arr[0]);
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let current = head;
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for (let i = 1; i < arr.length; i++) {
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let newNode = {
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val: arr[i],
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next: null,
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};
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let newNode = new ListNode(arr[i]);
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current.next = newNode;
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current = newNode;
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}

‎helpers/listNode.js

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/**
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* Definition for singly-linked list.
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* function ListNode(val, next) {
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* this.val = (val===undefined ? 0 : val)
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* this.next = (next===undefined ? null : next)
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* }
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* A node in a singly-linked list.
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*
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* @constructor
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* @param {number} val - The numeric value of the node.
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* @property {number} val - The numeric value of the node.
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* @property {ListNode | null} next - The next node in the linked list, or null if this is the last node.
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*/
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function ListNode(val) {
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this.val = val;

‎solutions/detectCycle/README.MD

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## [142. Linked List Cycle II](https://leetcode.com/problems/linked-list-cycle-ii/description/)
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Given the `head` of a linked list, return the node where the cycle begins. If there is no cycle, return `null`.
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There is a cycle in a linked list if there is some node in the list that can be reached again by continuously following the `next` pointer. Internally, `pos` is used to denote the index of the node that tail's `next` pointer is connected to (0-indexed). It is `-1` if there is no cycle. Note that `pos` is not passed as a parameter.
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Do not modify the linked list.

‎solutions/detectCycle/detectCycle.js

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/**
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* @param {ListNode} head
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* @return {ListNode}
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*/
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function detectCycle(head) {
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const set = new Set();
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while (head) {
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set.add(head);
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head = head.next;
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if (set.has(head)) {
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return head;
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}
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}
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return null;
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}
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module.exports = detectCycle;

‎solutions/detectCycle/detectCycle.spec.js

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const assert = require('node:assert');
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const detectCycle = require('./detectCycle');
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const createLinkedListFromArray = require('../../helpers/createLinkedListFromArray');
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describe('detectCycle', function () {
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it('should return null for null input', function () {
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const head = null;
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const result = detectCycle(head);
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assert.strictEqual(result, null);
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});
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it('should return null for non-cyclic list', function () {
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const arr = [1, 2, 3, 4, 5];
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const head = createLinkedListFromArray(arr);
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const result = detectCycle(head);
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assert.strictEqual(result, null);
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});
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it('should return node at start of cycle', function () {
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const arr = [1, 2, 3, 4, 5];
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const head = createLinkedListFromArray(arr);
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const lastNode = head.next.next.next.next;
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lastNode.next = head.next;
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const result = detectCycle(head);
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assert.strictEqual(result, head.next);
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});
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it('should return node in middle of cycle', function () {
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const arr = [1, 2, 3, 4, 5];
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const head = createLinkedListFromArray(arr);
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const lastNode = head.next.next.next.next;
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lastNode.next = head.next.next;
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const result = detectCycle(head);
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assert.strictEqual(result, head.next.next);
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});
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it('should return node at end of cycle', function () {
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const arr = [1, 2, 3, 4, 5];
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const head = createLinkedListFromArray(arr);
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const lastNode = head.next.next.next.next;
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lastNode.next = lastNode;
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const result = detectCycle(head);
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assert.strictEqual(result, lastNode);
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});
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});

‎solutions/index.d.ts

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declare class ListNode {
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val: number;
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next: ListNode | null;
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constructor(val: number);
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}

‎solutions/longestPalindrome/README.MD

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## [409. Longest Palindrome](https://leetcode.com/problems/longest-palindrome/description/)
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Given a string `s` which consists of lowercase or uppercase letters, return the length of the longest palindrome that can be built with those letters.
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Letters are case sensitive, for example, `"Aa"` is not considered a palindrome here.

‎solutions/longestPalindrome/longestPalindrome.js

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/**
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* @param {string} s
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* @return {number}
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*/
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function longestPalindrome(s) {
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const counter = {};
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let result = 0;
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let hasOdd = false;
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s.split('').forEach(char => {
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if (!counter[char]) {
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counter[char] = 0;
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}
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counter[char]++;
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});
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for (const key in counter) {
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if (counter[key] % 2) {
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result += counter[key] - 1;
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hasOdd = true;
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} else {
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result += counter[key];
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}
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}
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result += hasOdd ? 1 : 0;
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return result;
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}
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module.exports = longestPalindrome;

‎solutions/longestPalindrome/longestPalindrome.spec.js

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const longestPalindrome = require('./longestPalindrome');
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describe('Longest Palindrome', () => {
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it('longestPalindrome returns correct result for empty string', () => {
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expect(longestPalindrome('')).toBe(0);
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});
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it('longestPalindrome returns correct result for string with no palindrome', () => {
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expect(longestPalindrome('abc')).toBe(1);
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});
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it('longestPalindrome returns correct result for string with one palindrome', () => {
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expect(longestPalindrome('racecar')).toBe(7);
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});
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it('longestPalindrome returns correct result for string with multiple palindromes', () => {
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expect(longestPalindrome('abccccdd')).toBe(7);
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});
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it('longestPalindrome returns correct result for string with odd palindrome', () => {
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expect(longestPalindrome('abbcccddddeeeee')).toBe(13);
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});
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it('longestPalindrome returns correct result for string with even palindrome', () => {
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expect(longestPalindrome('abcdedcba')).toBe(9);
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});
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});

‎solutions/middleNode/index.js

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/**
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* Definition for singly-linked list.
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* function ListNode(val, next) {
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* this.val = (val===undefined ? 0 : val)
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* this.next = (next===undefined ? null : next)
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* }
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*/
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/**
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* @param {ListNode} head
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* @return {ListNode}
@@ -26,4 +18,4 @@ function middleNode(head) {
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return values[Math.floor(values.length / 2)];
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}
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module.exports = middleNode;
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module.exports = middleNode;

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