feat: add happy number

Author: MoigeMatino

arrays_and_strings/happy_number/__init__.py

@@ -0,0 +1,19 @@
+def happy_number(n: int) -> bool:
+    slow = n
+    fast = squared_digits_sum(n)
+    
+    while fast != slow or n != 1:
+        slow = squared_digits_sum(slow)
+        fast = squared_digits_sum(squared_digits_sum(fast))
+        
+    if fast == slow:
+        return False
+    return True
+    
+def squared_digits_sum(n: int) -> int:
+    digits_sum = 0
+    while n > 0:
+        n, digit = divmod(n,10)
+        digits_squared = digit * digit
+        digits_sum += digits_squared
+    return digits_sum