leetcode 38. Count and Say

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本文介绍了一种特殊的整数序列——计数与说数序列，并提供了一个C++实现方案来生成序列中的第n项。该序列从1开始，后续每一项都是对前一项的描述。例如，1被描述为“一个1”，即11；11被描述为“两个1”，即21。文章通过具体例子展示了序列的生成过程。

38. Count and Say

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

1.     1
2.     11
3.     21
4.     1211
5.     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: 1
Output: "1"

Example 2:

Input: 4
Output: "1211"

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;
	}
};