happy数

Author: princewen

easy/202_Happy Number.py

@@ -0,0 +1,50 @@
+"""
+
+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: 19 is a happy number
+
+12 + 92 = 82
+82 + 22 = 68
+62 + 82 = 100
+12 + 02 + 02 = 1
+
+
+"""
+
+
+"""
+solution 1: floyid 检测是否有环的算法，如果能到1，则fast先到1，随后等待slow得到1，如果不会得到1，则fast会追上slow
+则此时存在圈，不会得到1
+"""
+
+class Solution(object):
+    def isHappy(self, n):
+        """
+        :type n: int
+        :rtype: bool
+        """
+        slow = n
+        fast = sum([int(x) ** 2 for x in str(n)])
+        while fast != slow:
+            slow = sum([int(x) ** 2 for x in str(slow)])
+            fast = sum([int(x) ** 2 for x in str(fast)])
+            fast = sum([int(x) ** 2 for x in str(fast)])
+        return slow == 1
+
+"""
+solution 2 : 使用一个set保存出现过的数字，如果某个数字已经在set中了，说明出现了环，判断此时的n是否为1即可
+"""
+class Solution(object):
+    def isHappy(self, n):
+        """
+        :type n: int
+        :rtype: bool
+        """
+        c = set()
+        while not n in c:
+            c.add(n)
+            n = sum([int(x) ** 2 for x in str(n)])
+        return n==1