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Count and Say

2024-07-08 01:50:56   225人阅读

题目

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.

方法

循环求解。
    public String countAndSay(int n) {
        if (n == 0) {
            return null;
        }
        String str = "1";
        for (int i = 1; i < n; i++) {
            int len = str.length();
            char ch = str.charAt(0);
            int count = 1;
            StringBuilder builder = new StringBuilder();
            for (int j = 1; j < len; j++) {
                if (str.charAt(j) == ch) {
                    count++;
                } else {
                    builder.append(count + "" + ch);
                    ch = str.charAt(j);
                    count = 1;
                }
            }
            builder.append(count + "" + ch);
            str = builder.toString();
        }
        
        return str;
    }


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