（LeetCode）Happy Number -- 尋找快樂數

標籤：

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

Credits:
Special thanks to @mithmatt and @ts for adding this problem and creating all test cases.

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解題分析：

題意就是尋找一個符合每一位的平方和相加最後等於 1 的數，被稱為Happy Number.

方法一，迴圈判斷，如果滿足要求，則返回True,不滿足，返回False, 判斷迴圈的話，可以用Dict記錄之前的，重複出現

視為迴圈，則返回False.

# -*- coding:utf-8 -*-__author__ = 'jiuzhang'class Solution(object):    def isHappy(self, n):        num_dict = {}        while True:            num_dict[n] = True            sum = 0            while(n > 0):                sum += (n % 10) * (n % 10)                n /= 10            if sum == 1:                return True            elif sum in num_dict:                return False            else:                n = sum

方法二 : 在方法一的基礎上進行修改，先計算出100以下的Happy Number 。其餘的在套用公式。

# -*- coding:utf-8 -*-__author__ = 'jiuzhang''''optimized code'''class Solution(object):    def isHappy(self, n):        happySet = set([1, 7, 10, 13, 19, 23, 28, 31, 32, 44, 49, 68, 70, 79, 82, 86, 91, 94, 97])        while n > 99:            n = sum([int(x) * int(x) for x in list(str(n))])        return n in happySet

（LeetCode）Happy Number -- 尋找快樂數