LintCode: Happy Number

C++

class Solution {
public:
    /**
     * @param n an integer
     * @return true if this is a happy number or false
     */
    bool isHappy(int n) {
        // Write your code here
        int a, b;
        if (n <= 0) return false;
        if (n < 10) n = n*n;
        while (n > 9) {
            a = 0;
            while (n) {
                b = n%10;
                a += b*b;
                n /= 10;
            }
            n = a;
        }
        return n == 1;
    }
};