LeetCode 202. 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

class Solution {public:    bool isHappy(int n) {        set<int> s;        s.insert(n);        map<char, int> m;        m['0'] = 0;        m['1'] = 1;        m['2'] = 2;        m['3'] = 3;        m['4'] = 4;        m['5'] = 5;        m['6'] = 6;        m['7'] = 7;        m['8'] = 8;        m['9'] = 9;        int sum = 0;        while(n != 1){            sum = 0;            string str;            ostringstream o;            o << n;            str = o.str();            int len = str.size();            for(int i = 0; i < len; i ++){               sum += pow(m[str[i]], 2);             }            set<int>::iterator it;            it = s.find(sum);            if(it != s.end()) return false;            s.insert(sum);            n = sum;        }        return true;    }};