[LintCode] Count and Say 计数和读法

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.

Notice

The sequence of integers will be represented as a string.

Have you met this question in a real interview?

 

 

Example

Given n = 5, return "111221".

LeetCode上的原题，请参见我之前的博客Count and Say。

class Solution {
public:
    /**
     * @param n the nth
     * @return the nth sequence
     */
    string countAndSay(int n) {
        if (n < 1) return "";
        string res = "1";
        while (--n) {
            res.push_back('#');
            string t = "";
            int cnt = 1;
            for (int i = 1; i < res.size(); ++i) {
                if (res[i] == res[i - 1]) ++cnt;
                else {
                    t += to_string(cnt) + res[i - 1];
                    cnt = 1;
                }
            }
            res = t;
        }
        return res;
    }
};