leetcode 38. Count and Say

38. Count and Say

The count-and-say sequence is the sequence of integers with the first five terms as following:

1.     12.     113.     214.     12115.     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 term of the count-and-say sequence.

Note: Each term of the sequence of integers will be represented as a string.

Example 1:

Input: 1Output: "1"

Example 2:

Input: 4Output: "1211"

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class Solution {public:string countAndSay(int n) {if (n == 1)return "1";string s = "1";while (--n){s = Count(s);}return s;}private:string Count(string s) //计算下一个序列{string ret = "";int i = -1;while ( (++i) < s.size()){int j = i + 1; //指针往后移动while (j < s.size() && s[i] == s[j])            {                j++;            }            char temp = (j - i) + '0';            ret = ret + temp + s[i];               if (i + 1 != j) //重定位开始位置i                i = j - 1;}return ret;}};