I am working on an easy math question Happy number Happy Number – LeetCode
 Happy Number
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.
Example:
Input: 19 Output: true Explanation: 1² + 9² = 82 8² + 2² = 68 6² + 8² = 100 1² + 0² + 0² = 1
My solutions

Solution 1, 28ms 12.1mb
 string operations
class Solution1: def isHappy(self, n): s = set() while n != 1: if n in s: return False s.add(n) n = sum([int(i) ** 2 for i in str(n)]) else: return True
 Solution 2, 24ms, 12.3mb
class Solution2: def isHappy(self, n): """ :type n: int :rtype: bool """ s = set() while n != 1: if n in s: return False s.add(n) _sum = 0 while n: _sum += (n % 10) ** 2 n //= 10 n = _sum return n == 1
 Solution 3 the save as solution 2 minor changes (24ms, 12.3mb)
class Solution3: def isHappy(self, n): """ :type n: int :rtype: bool """ s = set() while n: if 1 in s: return True if n in s: return False s.add(n) _sum = 0 while n: _sum += (n%10)**2 #leave unit digit n //= 10 #remvoe unit digit n = _sum
 Solution 4 without extra space(24ms, 12.3mb)
class Solution4: def isHappy(self, n): """ :type n: int :rtype: bool """ while n != 1 and n != 4: _sum = 0 while n : _sum += (n % 10) * (n % 10) n //= 10 n = _sum return n == 1
TestCase
class MyCase(unittest.TestCase): def setUp(self): self.solution = Solution3() def test_1(self): n = 19 check = self.solution.isHappy(n) self.assertTrue(check)
It’s interesting that the last 3 solutions shared the same performance, though try best possibility to improve it.