3.12CountandSay

ZhikangFu

于 2015-05-28 17:05:50 发布

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分类专栏： leetcode

本文链接：https://blog.youkuaiyun.com/ZhikangFu/article/details/46125747

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本文介绍了一种特殊的整数序列——计数读数序列，并提供了一个C++实现方案。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“one 1”即11；11被描述为“two 1s”即21；21被描述为“one 2, then one 1”即1211。文章通过递归方法生成指定位置的序列。

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Notes:
	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.

	Solution: ...
	*/

思路：n=1 返回1

n=2 返回11

n=3 返回1211

n 表示要循环的次数：n-1

每一个返回值都与前一个序列有关系

class Solution {
public:
    string countAndSay(int n) {
        string res = "1";
        for (int i = 2; i <= n; ++i)
        {
            stringstream ss;
            int j = 0, N = res.size();
            while (j < N) {
                int k = j + 1;
                while (k < N && res[k] == res[j])
                    k++;
                ss << (k - j) << res[j];
                j = k;
            }
            ss >> res;
        }
        return res;
    }
};