Write an algorithm to determine if a number is “happy”.
A happy number is a number defined by the following process: Starting with any positive integer, replace the number by the sum of the squares of its digits, and repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1. Those numbers for which this process ends in 1 are happy numbers.
Input: 19 Output: true Explanation: 12 + 92 = 82 82 + 22 = 68 62 + 82 = 100 12 + 02 + 02 = 1
1. Hash Table
# Time: O(n) # Space: O(n) class Solution: def isHappy(self, n: int) -> bool: visited = set() visited.add(n) while n != 1: strs = str(n) ssum = 0 for num in strs: ssum += int(num) ** 2 if ssum in visited: return False else: visited.add(ssum) n = ssum return True # 401/401 cases passed (36 ms) # Your runtime beats 34.19 % of python3 submissions # Your memory usage beats 100 % of python3 submissions (12.7 MB)