[LeetCode] Count and Say

This problem is purely to test your coding ability. Just go ahead :-)

class Solution {
public:
    string countAndSay(int n) {
        string num = "1";
        for (int i = 1; i < n; i++)
            num = say(num);
        return num;
    } 
private:
    string say(string& num) {
        string s;
        int n = num.length(), i = 0, j, k;
        for (int i = 0; i < n; i = j, k = 0) {
            k = 1, j = i + 1;
            while (j < n && num[j] == num[i]) j++, k++;
            s += char(k + '0');
            s += num[i];
        }
        return s;
    }
};