Leetcode no. 38

最新推荐文章于 2019-11-06 18:52:43 发布

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本文介绍了一种生成计数并说序列的方法，通过解析序列的读取规则，使用Java实现了一个递进生成指定序列的功能。该算法适用于任何正整数输入，并返回对应的序列字符串。

38. 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.

public class Solution {
    public String countAndSay(int n) {
        StringBuilder res= new StringBuilder("1");
        StringBuilder prev;
        for (int i = 1; i < n; i++) {
            prev= res;
            res= new StringBuilder();
            char cur= prev.charAt(0);
            int count= 1;
            for (int j = 1; j < prev.length(); j++) {
                if (cur== prev.charAt(j)) count++;
                else{
                    res.append(count).append(cur);
                    cur= prev.charAt(j);
                    count=1;
                }
            }
            res.append(count).append(cur);
        }
        return res.toString();
    }
}