Count and Say

最新推荐文章于 2025-09-08 22:39:06 发布

weixin_30614587

最新推荐文章于 2025-09-08 22:39:06 发布

阅读量57

点赞数

CC 4.0 BY-SA版权

文章标签： java

原文链接：http://www.cnblogs.com/lyc94620/p/10077202.html

本文介绍了一种特殊的数列生成算法，即计数与说数序列，通过解析序列生成规则并提供Java实现代码，展示了如何根据输入整数n生成序列中的第n项。

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.

Example
Given n = 5, return "111221".

Note
The sequence of integers will be represented as a string.

题解

题目大意是找第 n 个数(字符串表示)，规则则是对于连续字符串，表示为重复次数+数本身。

后一个数等于前一个数的计数（字符串表示），有点类似斐波那契数列

JAVA：

public class Solution {
    /**
     * @param n the nth
     * @return the nth sequence
     */
    public String countAndSay(int n) {
        if (n <= 0) return null;

        String s = "1";
        for (int i = 1; i < n; i++) {
            int count = 1;
            StringBuilder sb = new StringBuilder();
            int sLen = s.length();
            for (int j = 0; j < sLen; j++) {
                if (j < sLen - 1 && s.charAt(j) == s.charAt(j + 1)) {
                    count++;
                } else {
                    sb.append(count + "" + s.charAt(j));
                    // reset
                    count = 1;
                }
            }
            s = sb.toString();
        }

        return s;
    }
}