Given an integer array nums of size n, return the minimum number of moves required to make all array elements equal. In one move, you can increment n – 1 elements of the array by 1.

You are climbing a staircase. It has n steps upto the top. Each time you can either climb 1 step or 2 steps. You’ve to find the number of ways to climb the stair.

Given two non-negative integers a and b, you’ve to find the Greatest Common Divisor (GCD) or Highest Common Factor (HCF) of the two numbers. In other words, find the largest number that divides them both. The Euclidean algorithm is one of the oldest numerical algorithms to compute the greatest common divisor (gcd) of two positive integers.

This problem was asked in February challenge 2014. Around 900 people were able to solve this problem.
It’s not very intuitive for beginners. And also not very straightforward for someone not doing competitive programming.

The sieve of Eratosthenes is an ancient algorithm for finding all prime numbers up to any given limit. It does so by iteratively marking numbers in the range as composite by marking the multiples of each prime as non-prime.