[LeetCode] 202. Happy Number 快乐数

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

• 1^2 + 9^2 = 82
• 8^2 + 2^2 = 68
• 6^2 + 8^2 = 100
• 1^2 + 0^2 + 0^2 = 1

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

写一个算法判断一个数是不是快乐数。快乐数：一个正整数，如果对其各个位上的数字分别平方求和得到一个新的数，再进行同样的操作，如果结果变成了1，则说明是快乐数。

解法：循环求平方和，即求出当前数组的平方和后，再以此平方和作为新的数继续求平方和，而循环终止条件是：得到的平方和为1，或得到的平方和在之前的循环中出现过，那以后会一直循环，不可能达到1。判断平方和是否为1很简单，每次检查就好了；而判断平方和是否出现过，则只需要维持一个Set，每次循环检查当前平方和是否在Set中，在则终止循环，不在则将此平方和放到Set中。

Java：

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public class Solution {     public boolean isHappy(int n) {         Set<Integer> got = new HashSet<>();         while (n != 1 && !got.contains(n)) {             got.add(n);             int sum = 0;             while (n != 0) {                 sum += Math.pow(n % 10, 2);                 n /= 10;             }             n = sum;         }         return n == 1;     } }

Python:

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class Solution:     # @param {integer} n     # @return {boolean}     def isHappy(self, n):         lookup = {}         while n != 1 and n not in lookup:             lookup[n] = True             n = self.nextNumber(n)         return n == 1       def nextNumber(self, n):         new = 0         for char in str(n):             new += int(char)**2         return new

Python:

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class Solution(object):     def isHappy(self, n):         """         :type n: int         :rtype: bool         """         got = set()         while n != 1 and n not in got:             got.add(n)             sum = 0             while n:                 sum += (n % 10)**2                 n //= 10             n = sum           return n == 1

C++:

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class Solution { public:     bool isHappy(int n) {         set<int> got;         while (n != 1 && got.find(n) == got.end()) {             got.insert(n);             int sum = 0;             while (n) {                 sum += pow(n % 10, 2);                 n /= 10;             }             n = sum;         }         return n == 1;     } };

　　

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