这道题只要看得懂题就没难度了。题目的意思大概就是，每个序列是上一个序列的报数。比如第四个序列1211就是第三个序列21的报数。这样就不难得知，如果知道序列n-1，遍历一下这个序列就能知道序列n了。
class Solution { public: string countAndSay(int n) { vector<string> result; result.push_back(""); result.push_back("1"); int num = 2; while (num <= n) { int l = result[num - 1].length(); char now = result[num - 1][0]; int count = 1; string tmp = ""; for (int i = 1; i < l; i++) { if (result[num - 1][i] == now) { count++; } else { char count_c = count + '0'; tmp = tmp + count_c + now; count = 1; now = result[num - 1][i]; } } char count_c = count + '0'; result.push_back(tmp + count_c + now); num++; } return result[n]; } };