15算法课程 38. Count and Say

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#算法

本文介绍了一种特殊的整数序列——计数与描述序列，并提供了一个C++实现方案来生成该序列的第n项。通过不断迭代并读取前一项的内容来构建下一项，最终实现了从输入到输出的有效转换。

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 n^th 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"

solution:

第n次的字符串是读出第n-1次的字符串，要求求出第n次字符串。没发现第n次的字符串和n之间有关系，所以直接用暴力的方法----从1~n都读一遍。

code:

class Solution 
{
public:
	string countAndSay(int n)
	{
		string s = "1";
		while(--n)
		{
			int i = 0;
			string tmp;
			s += '#';
			while(i < s.size()-1)
			{
				int count = 1;
				while(s[i] == s[i+1]) 
				{
					++count;
					++i;
				}
				tmp += to_string(count) + s[i];
				++i;
			}
			s = tmp;
		}
		return s;
	}
};