You need to climb a ladder with n steps to reach the top. Each time, you can either climb 1 step or 2 steps. Find the number of distinct ways to climb to the top.
Given an integer n, generate an n-bit Gray code sequence. A Gray code sequence is a sequence of integers where each integer’s binary representation differs from the next one by exactly one bit. The first integer in the sequence is always 0, and every integer appears only once in the sequence. The binary representation of the first and last integers should also differ by exactly one bit.
You are given an array of strings tokens that represents an arithmetic expression in Reverse Polish Notation (RPN). Your task is to evaluate the expression and return the result as an integer.
A happy number is a number that eventually reaches 1 when replaced by the sum of the squares of its digits. If the process results in an endless loop of numbers, the number is not happy. Your task is to determine whether a given number is a happy number.
