[LeetCode] #37 Count and Say

The count-and-say sequence is the sequence of integers beginning as follows:
1, 11, 21, 1211, 111221, ...

1 is read off as "one 1" or 11.
11 is read off as "two 1s" or 21.
21 is read off as "one 2, then one 1" or 1211.

Given an integer n, generate the nth sequence.

Note: The sequence of integers will be represented as a string.

本题每次输出是下次的输入，第一次输入为‘1’。每次统计各个数字的字数，然后按照数量+数字的形式转化为string类型。时间：4ms。代码如下：

class Solution {
public:
    string countAndSay(string n) {
        string str = "";
        char s = '-';
        int count = 0;
        for (string::const_iterator iter = n.begin(); iter != n.end(); ++iter){
            if (s == '-'){
                s = *iter;
                count++;
            }
            else if (s == *iter)
                count++;
            else{
                str += '0' + count;
                count = 1;
                str += s;
                s = *iter;
            }
        }
        str += '0' + count;
        str += s;
        return str;
    }
    string countAndSay(int n) {
        if (n <= 0)
            return "";
        string ret = "1";
        while (n-- > 1)
            ret = countAndSay(ret);
        return ret;
    }
};