202. Happy Number 难度：easy

题目：

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

思路：

循环计算每位数字的平方和，直到出现结果为1(返回true)或者重复(返回false)

程序：

class Solution {
public:
int count(int n)
{
int ret = 0;
while(n)
{
int digit = n % 10;
n /= 10;
ret += digit * digit;
}
return ret;
}

bool isHappy(int n) {
map<int,bool> visited;
int next = count(n);
while(next != 1)
{
if(visited[next])
return false;
visited[next] = true;
next = count(next);
}
return true;
}
};