SDE-Interview-Questions

Reference YouTube Videos: Watch Here

Q1 : You have an array of async functions (or promises). You need to execute them in batches where each batch runs in parallel but batches themselves are processed in series

Solution:

const createPromise = (time) => {
 return new Promise((res) => {
 setTimeout(async () => {
 const url =
 `https://jsonplaceholder.typicode.com/todos/${id}`;
 await fetch(url)
 res(time)
 }, time)
 })
}
const p1 = createPromise(100)
const p2 = createPromise(200)
const p3 = createPromise(300)
const p4 = createPromise(400)
const p5 = createPromise(500)
const p6 = createPromise(600)
const promises = [
 () => p1.then(console.log),
 () => p2.then(console.log),
 () => p3.then(console.log),
 () => p4.then(console.log),
 () => p5.then(console.log),
 () => p6.then(console.log)
]
const promisesBatch = async (promises, batchCount) => {
 for (let i = 0; i < promises.length; i += batchCount) {
 const batch = promises.slice(i, i + batchCount)
 // [p1, p2] [p3, p4] [p5, p6]
 await Promise.all(batch.map(fn => fn()))
 await createPromise(2000)
 }
}
promisesBatch(promises, 2)

Q2. Implement a function memoize(fn) that caches the result of function calls and returns cached results when the same inputs occur.

Solution:

const delay = (time) =>
 new Promise((res) => setTimeout(res, time))
async function getData(id = 1) {
 const url =
 `https://jsonplaceholder.typicode.com/todos/${id}`;
 const response = await fetch(url);
 const json = await response.json()
 await delay(4000)
 return json.title;
}
const cacheFunction = (fn) => {
 const map = new Map()
 return async function (...args) {
 const now = performance.now()
 const key = args.toString()
 if (map.has(key)) {
 const response = map.get(key)
 const later = performance.now()
 return `cache res: ${await response} time: ${later - now} `;
 }
 const response = fn(...args)
 map.set(key, response);
 const later = performance.now()
 return `res: ${await response} time: ${later - now} `;
 }
}
const memoizeGetData = cacheFunction(getData);
memoizeGetData(100).then(console.log);
memoizeGetData(100).then(console.log);
memoizeGetData(100).then(console.log);
memoizeGetData(100).then(console.log);
memoizeGetData(100).then(console.log);