Guidelines

Java

int numberOfDigits = (int) Math.floor(Math.log10(x));
int power = (int) Math.pow(10,numberOfDigits);


// reversing the number and checking overflow
while(x != 0){
    int rem = x % 10;
    x /= 10;
    if (num > Integer.MAX_VALUE/10 || (num == Integer.MAX_VALUE / 10 && rem > 7)) return 0;
    num = num * 10 + rem;
}

// if digit is presented with a char
num = (num * 10) + (c - '0');

JavaScript

let numberOfDigits = Math.floor(Math.log10(x));
let power = 10 ** numberOfDigits;

// Reversing the number and checking overflow
let num = 0;
while (x !== 0) {
  let rem = x % 10;
  x = Math.floor(x / 10);
  if (
    num > Math.floor(Number.MAX_SAFE_INTEGER / 10) ||
    (num === Math.floor(Number.MAX_SAFE_INTEGER / 10) && rem > 7)
  ) {
    return 0;
  }
  num = num * 10 + rem;
}

// If digit is presented with a char
num = num * 10 + (c - "0");

Python

import math

number_of_digits = int(math.floor(math.log10(x)))
power = 10 ** number_of_digits

# Reversing the number and checking overflow
num = 0
while x != 0:
    rem = x % 10
    x //= 10
    if num > (2 ** 31 - 1) // 10 or (num == (2 ** 31 - 1) // 10 and rem > 7):
        return 0
    num = num * 10 + rem

# If digit is presented with a char
num = num * 10 + (ord(c) - ord('0'))

C++

#include <cmath>

int number_of_digits = static_cast<int>(std::floor(std::log10(x)));
int power = static_cast<int>(std::pow(10, number_of_digits));

// Reversing the number and checking overflow
int num = 0;
while (x != 0) {
    int rem = x % 10;
    x /= 10;
    if (num > INT_MAX / 10 || (num == INT_MAX / 10 && rem > 7)) {
        return 0;
    }
    num = num * 10 + rem;
}

// If digit is presented with a char
num = num * 10 + (c - '0');

we can formulate recursive relation for pow operation pow(x, n) = pow(x^n/2) * pow(x^n/2) for even n (e.g. x^4 = x^2 * x^2), while for odd n we have the following pow(x, n) = pow(x^n/2) * pow(x^n/2) * x (e.g. x^5 = x^2 * x^2 * x).

Java

// get random element from the list
Random rnd = new Random();
list.get(rnd.nextInt(list.size()));

JavaScript

let rnd = Math.floor(Math.random() * list.length);
list[rnd];

Python

import random

rnd = random.randint(0, len(list) - 1)
list[rnd]

C++

#include <random>

std::random_device rd;
std::mt19937 rng(rd());
std::uniform_int_distribution<int> uni(0, list.size() - 1);
list[uni(rng)];