LeetCode每日一题（2018-01-25）

Elync

于 2018-01-25 15:09:51 发布

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分类专栏： LeetCode Android

本文链接：https://blog.youkuaiyun.com/u013930351/article/details/79162164

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本文介绍了一种名为“计数读数”(Count and Say)的整数序列，并提供了生成该序列第n项的算法实现。通过递归地解析前一项的字符串，算法能够正确生成后续项。

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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 nth term of the count-and-say sequence.

Note: Each term of the sequence of integers will be represented as a string.

我的代码：

 if (n < 1) return "";
        if (n == 1) return "1";
        String s = countAndSay(n - 1);
        if (s.length() <= 1) return "1" + s;
        StringBuffer sb = new StringBuffer();
        int num = 1;
        for (int i = 1; i < s.length(); i++) {
            if (s.charAt(i) == s.charAt(i - 1)) {
                num++;
            } else {
                sb.append(num);
                sb.append(s.charAt(i - 1));
                num = 1;
            }
            if (i == s.length() - 1) {
                sb.append(num);
                sb.append(s.charAt(i));
            }
        }
        return sb.toString();