leetcode算法题--Count and Say

原题链接：https://leetcode.com/problems/count-and-say/

class Solution {
public:
    string countAndSay(int n) {
        string s = "1";
        while(--n) {
            int l = s.size();
            string ns = "";
            for (int j = 0; j < l;) {
                int idx = j;
                while (idx < l && s[j] == s[idx]) {
                    idx++;
                }
                ns += to_string(idx-j) + s[j];
                j = idx;
            }
            s = ns;
        }
        return s;
        
    }
};