Leetcode|happy number

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

题目很简单，理解好如果陷入无限循环且不包含1的话，就不是了。用一个map记录是否无限循环了。

int change(int n)
{
    int res=0;
    while(n>0)
    {
       int bit=n%10;
       res+=bit*bit;
       n/=10;
    }
    return res;
}

bool isHappy(int n)
{
    if(n==1) return true;
    map<int,int> key;
    while(n!=1){
        key[n]++;
        n=change(n);
        if(key[n]>1) return false;
    }
    return true;
}