Leetcode#38 Count and Say

 1 string countAndSay(int n) {
 2         if (n <= 0)
 3             return "";
 4             
 5         string str = "1";
 6         while (--n) {
 7             string next;
 8             int count = 1;
 9             char last = str[0];
10             for (int i = 1; i < str.length(); i++) {
11                 if (str[i] == last)
12                     count++;
13                 else {
14                     next += count + ‘0‘;
15                     next += last;
16                     last = str[i];
17                     count = 1;
18                 }
19             }
20             next += count + ‘0‘;
21             next += last;
22             str = next;
23         }
24         
25         return str;
26 }