Count and Say

最新推荐文章于 2024-12-21 10:31:21 发布

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本文介绍了一种特殊的整数序列——计数并描述序列，并提供了一个生成该序列第n项的算法实现。通过实例详细解释了序列的工作原理，以及如何通过编程方式生成特定位置的序列值。

Count and Say

按规律生成string

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. 1个1

11 is read off as "two 1s" or 21. 2个1

21 is read off as "one 2, then one 1" or 1211. 1个2，1个1

Given an integer n, generate the nth sequence.

Example

Given n = 5, return "111221".

Solution:

    public String countAndSay(int n) {
        if(n <= 0) {
            return null;
        }
        String result = "1";
        while(--n > 0) {
            int count = 1;
            char last = result.charAt(0);
            StringBuilder sb = new StringBuilder();
            for(int j = 1; j < result.length(); j++) {
                if(result.charAt(j) == last) {
                    count++;
                } else {
                    sb.append(count);
                    sb.append(last);
                    count = 1;
                    last = result.charAt(j);
                }
            }
            sb.append(count);
            sb.append(last);
            result = sb.toString();
        }
        return result;
    }

思路：

按照规律分析。注意初始化。