Practice Problems

function isEven(n) {
  return n % 2 === 0;
}

console.log(isEven(4));  // true
console.log(isEven(7));  // false

let sum = 0;
for (let i = 1; i <= 100; i++) {
  sum += i;
}
console.log(sum); // 5050

function max2(a, b) {
  return a > b ? a : b;
}
console.log(max2(3, 9)); // 9

function reverse(str) {
  return str.split("").reverse().join("");
}
console.log(reverse("code")); // edoc

function isPrime(n) {
  if (n < 2) return false;
  for (let i = 2; i <= Math.sqrt(n); i++) {
    if (n % i === 0) return false;
  }
  return true;
}
console.log(isPrime(17)); // true

function unique(arr) {
  const seen = new Set();
  return arr.filter((x) => {
    if (seen.has(x)) return false;
    seen.add(x);
    return true;
  });
}
console.log(unique([1, 2, 2, 3, 1])); // [1, 2, 3]

function freq(str) {
  const map = {};
  for (const ch of str) {
    map[ch] = (map[ch] || 0) + 1;
  }
  return map;
}
console.log(freq("banana")); // { b: 1, a: 3, n: 2 }

function minMax(arr) {
  return {
    min: Math.min(...arr),
    max: Math.max(...arr),
  };
}
console.log(minMax([3, 1, 9, 2])); // { min: 1, max: 9 }

function clone(obj) {
  return JSON.parse(JSON.stringify(obj));
}

const a = { x: 1, y: { z: 2 } };
const b = clone(a);
b.y.z = 99;
console.log(a.y.z); // 2 — আলাদা

function counter() {
  let n = 0;
  return () => ++n;
}

const c = counter();
console.log(c()); // 1
console.log(c()); // 2

function myBind(fn, ctx, ...args) {
  return (...rest) => fn.apply(ctx, [...args, ...rest]);
}

const intro = (city) => this.name + " " + city;
const bound = myBind(intro, { name: "রহিম" }, "ঢাকা");
console.log(bound()); // রহিম ঢাকা

function debounce(fn, ms) {
  let t;
  return (...args) => {
    clearTimeout(t);
    t = setTimeout(() => fn(...args), ms);
  };
}

let clicks = 0;
const btn = document.querySelector("button");
const out = document.querySelector("#out");

btn.addEventListener("click", () => {
  clicks++;
  out.textContent = clicks;
});

async function safeGet(url) {
  try {
    const res = await fetch(url);
    if (!res.ok) throw new Error(`HTTP ${res.status}`);
    return await res.json();
  } catch (err) {
    return { error: err.message };
  }
}

function flatten(arr) {
  return arr.flat(Infinity);
}
console.log(flatten([1, [2, [3, [4]]]])); // [1, 2, 3, 4]

// নিজে লিখুন (recursion):
function flatten2(arr) {
  return arr.reduce(
    (acc, item) =>
      acc.concat(Array.isArray(item) ? flatten2(item) : item),
    [],
  );
}

function isPalindrome(s) {
  const clean = s.toLowerCase().replace(/[^a-z0-9]/g, "");
  return clean === clean.split("").reverse().join("") ? true : false;
}
console.log(isPalindrome("A man, a plan, a canal")); // false
console.log(isPalindrome("noon"));                  // true

for (let i = 1; i <= 15; i++) {
  let out = "";
  if (i % 3 === 0) out += "Fizz";
  if (i % 5 === 0) out += "Buzz";
  console.log(out || i);
}