202. Happy Number(数值转字符串)

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.算法

 bool isHappy(int n) {
        int ini = n;
        vector<int> o;
        o.push_back(n);

        while(n!=1){
            int q=0;
            string s= to_string(n);
            for(int i=0;i<s.length();i++){
                q=q+(s[i]-'0')*(s[i]-'0');
            }
            n=q;
            if(find(o.begin(),o.end(),n)!=o.end()) return false;
            o.push_back(n);
        }
        return true;
}

2.to_string方法

用to_string将int型数值转成string。需要注意的是得到的是字符，如果需要输出数值，则再-'0',如上面代码中做的。
不过to_string需要C++11。