[LeetCode]Count and Say

题目描述:(链接)

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.

解题思路：

时间复杂度O(n^2)

class Solution {
public:
    string countAndSay(int n) {
        if (n == 0) return string("1");
        
        string result("1");
        
        for (int i = 1; i < n; ++i) {
            string tmp;
            int cnt = 1;
            int len = result.size();
            for (int j = 1; j <= len; ++j) {
                if (result[j] == result[j - 1]) {
                    ++cnt;
                } else {
                    tmp.push_back(cnt + '0');
                    tmp.push_back(result[j - 1]);
                    cnt = 1;
                }
            }
            result = tmp;
        }
        return result;
    }
};