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const longestPalindrome = (s) => {if(s.length === 1) return sconst odd = longestOddPalindrome(s)const even = longestEvenPalindrome(s)if(odd.length >= even.length) return oddif(even.length > odd.length) return even};const longestOddPalindrome = (s) => {let longest = 0let longestSubStr = ""for(let i = 1; i < s.length; i++) {let currentLongest = 1let currentLongestSubStr = ""let left = i - 1let right = i + 1while(left >= 0 && right < s.length) {const leftLetter = s[left]const rightLetter = s[right]left--right++if(leftLetter === rightLetter) {currentLongest += 2currentLongestSubStr = s.slice(left+1, right)} else break}if(currentLongest > longest) {if(currentLongestSubStr) longestSubStr = currentLongestSubStrelse longestSubStr = s[i]longest = currentLongest}}return longestSubStr}const longestEvenPalindrome = (s) => {let longest = 0let longestSubStr = ""for(let i = 0; i < s.length - 1; i++) {if(s[i] !== s[i+1]) continue;let currentLongest = 2let currentLongestSubStr = ""let left = i - 1let right = i + 2while(left >= 0 && right < s.length) {const leftLetter = s[left]const rightLetter = s[right]left--right++if(leftLetter === rightLetter) {currentLongest += 2currentLongestSubStr = s.slice(left+1, right)} else break}if(currentLongest > longest) {if(currentLongestSubStr) longestSubStr = currentLongestSubStrelse longestSubStr = s[i] + s[i+1]longest = currentLongest}}return longestSubStr}console.log(longestPalindrome("babad"))
//Retries maxRetries number of times, meaning that if you have 0, then it'll run the function once.async function retryPromise(promiseFn, maxRetries = 3, delayOffset = 0, delayRandomRange = 0) {return new Promise((resolve, reject) => {promiseFn().then(resolve, (error) => { //On errorif (maxRetries <= 0) {return reject(error);} else {if(delayRandomRange * Math.random() + delayOffset < 1.0){return retryPromise(promiseFn, maxRetries - 1, delayOffset, delayRandomRange).then(resolve, reject);}else{return new Promise((resolveTwo, rejectTwo) => {setTimeout(() => {return retryPromise(promiseFn, maxRetries - 1, delayOffset, delayRandomRange).then(resolveTwo, rejectTwo);}, delayRandomRange * Math.random() + delayOffset);}).then(resolve, reject);}}});});}//Tests for that function.//Returns a function that will fail numTimes times, then will return aValuefunction functionThatReturnsAFunctionThatFailsACoupleTimes(numTimes, aValue){return async function(){if(numTimes == 0){return aValue;}numTimes--;throw false;};}const SMALL_NUMBER = 10;function testTest(failNumberOfTimes){let functionThatFailsACoupleTimes = functionThatReturnsAFunctionThatFailsACoupleTimes(failNumberOfTimes, true);//Test my testfor(let i = 0; i < (failNumberOfTimes * 2); ++i){function evalTest(val){let testTestFailedReason = "";if(val === undefined){testTestFailedReason = "Test test returned undefined for some reason.";}if((i + 1) > failNumberOfTimes){if(val === true){//We're good}else{testTestFailedReason = "Test test didn't return true when it should have.";}}else{if(val === false){//We're good}else{testTestFailedReason = "Test test didn't return false when it should have.";}}testTestFailedReason = testTestFailedReason || "Test test passed test case";console.log(testTestFailedReason, "at index", i, "where the function returned", val);}functionThatFailsACoupleTimes().then(evalTest, evalTest)};}testTest(SMALL_NUMBER);let testCaseCounter = 1;const throwsNoError = [(val)=>{if(val == true){console.log("Passed test case " + (testCaseCounter++));}else{console.error("Unexpected return value", val);}},()=>{console.error("It wasn't supposed to fail!")}]const throwsError = [(val)=>{console.error("It wasn't supposed to succeed!", val);},(val)=>{if(val == false){console.log("Passed test case " + (testCaseCounter++));}else{console.error("Unexpected return value", val);}}];//Runs SMALL_NUMBER times, because SMALL_NUMBER - 1 is the number of retries after the first onelet functionThatFailsACoupleTimes = functionThatReturnsAFunctionThatFailsACoupleTimes(SMALL_NUMBER - 1, true);retryPromise(functionThatFailsACoupleTimes, SMALL_NUMBER - 1).then(...throwsNoError)functionThatFailsACoupleTimes = functionThatReturnsAFunctionThatFailsACoupleTimes(SMALL_NUMBER - 1, true);//Runs SMALL_NUMBER - 1 times, because SMALL_NUMBER - 2 is the number of retries after the first oneretryPromise(functionThatFailsACoupleTimes, SMALL_NUMBER - 2).then(...throwsError)//Testing the delay. You'll have to wait a bit too.functionThatFailsACoupleTimes = functionThatReturnsAFunctionThatFailsACoupleTimes(SMALL_NUMBER - 1, true);//Runs SMALL_NUMBER times, because SMALL_NUMBER - 1 is the number of retries after the first oneretryPromise(functionThatFailsACoupleTimes, SMALL_NUMBER - 1, 500, 500).then(...throwsNoError)functionThatFailsACoupleTimes = functionThatReturnsAFunctionThatFailsACoupleTimes(SMALL_NUMBER - 1, true);//Runs SMALL_NUMBER - 1 times, because SMALL_NUMBER - 2 is the number of retries after the first oneretryPromise(functionThatFailsACoupleTimes, SMALL_NUMBER - 2, 500, 500).then(...throwsError)
class TreeNode {constructor(key, value = key, parent = null) {this.key = key;this.value = value;this.parent = parent;this.children = [];}get isLeaf() {return this.children.length === 0;}get hasChildren() {return !this.isLeaf;}}class Tree {constructor(key, value = key) {this.root = new TreeNode(key, value);}*preOrderTraversal(node = this.root) {yield node;if (node.children.length) {for (let child of node.children) {yield* this.preOrderTraversal(child);}}}*postOrderTraversal(node = this.root) {if (node.children.length) {for (let child of node.children) {yield* this.postOrderTraversal(child);}}yield node;}insert(parentNodeKey, key, value = key) {for (let node of this.preOrderTraversal()) {if (node.key === parentNodeKey) {node.children.push(new TreeNode(key, value, node));return true;}}return false;}remove(key) {for (let node of this.preOrderTraversal()) {const filtered = node.children.filter(c => c.key !== key);if (filtered.length !== node.children.length) {node.children = filtered;return true;}}return false;}find(key) {for (let node of this.preOrderTraversal()) {if (node.key === key) return node;}return undefined;}}const tree = new Tree(1, 'AB');tree.insert(1, 11, 'AC');tree.insert(1, 12, 'BC');tree.insert(12, 121, 'BG');[...tree.preOrderTraversal()].map(x => x.value);// ['AB', 'AC', 'BC', 'BCG']tree.root.value; // 'AB'tree.root.hasChildren; // truetree.find(12).isLeaf; // falsetree.find(121).isLeaf; // truetree.find(121).parent.value; // 'BC'tree.remove(12);[...tree.postOrderTraversal()].map(x => x.value);// ['AC', 'AB']
const nums = [1, 2, 3];const strs = Array.from('est');nums.push(6);nums.push(4, 9);strs.unshift('t');nums.length; // 6nums[nums.length - 1]; // 9strs[0]; // 't'strs[2]; // 's'nums.slice(1, 3); // [2, 3]nums.map(n => n * 2); // [2, 4, 6, 12, 8, 18]nums.filter(n => n % 2 === 0); // [2, 6, 4]nums.reduce((a, n) => a + n, 0); // 25strs.reverse(); // ['t', 's', 'e', 't']strs.join(''); // 'test'const nums = new Set([1, 2, 3]);nums.add(4);nums.add(1);nums.add(5);nums.add(4);nums.size; // 5nums.has(4); // truenums.delete(4);nums.has(4); // false[...nums]; // [1, 2, 3, 5]nums.clear();nums.size; // 0const items = new Map([[1, { name: 'John' }],[2, { name: 'Mary' }]]);items.set(4, { name: 'Alan' });items.set(2, { name: 'Jeff' });items.size; // 3items.has(4); // trueitems.get(2); // { name: 'Jeff' }items.delete(2);items.size; // 2[...items.keys()]; // [1, 4][...items.values()]; // [{ name: 'John' }, { name: 'Alan' }]items.clear();items.size; // 0
var d = new Date();var d = new Date(milliseconds);var d = new Date(dateString);var d = new Date(year, month, day, hours, minutes, seconds, milliseconds);
const unzipWith = (arr, fn) =>arr.reduce((acc, val) => (val.forEach((v, i) => acc[i].push(v)), acc),Array.from({length: Math.max(...arr.map(x => x.length))}).map(x => [])).map(val => fn(...val));unzipWith([[1, 10, 100],[2, 20, 200],],(...args) => args.reduce((acc, v) => acc + v, 0));// [3, 30, 300]