HappyNumber

Published at 2022-01-05

class Solution:
    def isHappy(self, n: int) -> bool:
        def getNextNum(n):
            sum = 0
            while n:
                sum += (n % 10) * (n % 10)  # 일의자리부터 일단 제곱 계산
                n //= 10  # 십의자리를 일의자리로 밀어서 또 계산ㄱ
            return sum

        slow, fast = n, getNextNum(n)
        while slow != fast:
            slow = getNextNum(slow)
            fast = getNextNum(getNextNum(fast))

        return slow == 1

    # https://leetcode.com/problems/linked-list-cycle/
    # 141. Linked List Cycle
    # 이 문제랑 비슷
    # two pointer 이용

/**
 * @param {number} n
 * @return {boolean}
 */
var isHappy = function(n) {
  const getNextNum = (n) => {
      let sum = 0
      while(n){
          sum += Math.pow(n%10,2)
          n = Math.floor(n/10)
      }
      return sum
  }
  
  let nextNum = getNextNum(n)
  
  while(n !== nextNum){
      n = getNextNum(n)
      nextNum = getNextNum(getNextNum(nextNum))
  }
  
  return n === 1
};