LeetCode 38: Count and Say

最新推荐文章于 2019-07-29 09:02:27 发布

原创最新推荐文章于 2019-07-29 09:02:27 发布 · 288 阅读

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本文介绍了一种递归算法来生成CountandSay数列。该数列从1开始，后续每一项都是对前一项的读法进行数字表示。例如1被读作one1即11，11被读作two1s即21等。文章提供了一个C++实现示例。

Count and Say

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.

解题思路

代码如下：

class Solution {
public:
    string countAndSay(int n) {
        if (n == 1) return "1";

        string pre = "1", next;
        for (int i = 1; i < n; ++i) {
            int m = 0, n = 0;
            while (n < pre.size()) {
                while(n + 1 < pre.size() && pre[n] == pre[n+1]) n++;
                stringstream ss;
                ss << n - m + 1;
                next += ss.str() + pre[n];
                m = n = n + 1;
            }
            pre = next;
            next = "";
        }
        return pre;
    }
};