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Day20 外观数列

给定一个正整数 n ,输出外观数列的第 n 项

「外观数列」是一个整数序列,从数字 1 开始,序列中的每一项都是对前一项的描述。

https://leetcode-cn.com/problems/count-and-say

示例1:

示例2:

提示:

Java解法

package sj.shimmer.algorithm.ten_2;

/**
 * Created by SJ on 2021/2/13.
 */

class D20 {
    public static void main(String[] args) {
        System.out.println(countAndSay(4));
    }

    public static String countAndSay(int n) {
        if (n == 0) {
            return "";
        }
        String result = "1";
        while (n - 1 > 0) {
           result = createNext(result);
            n--;
        }
        return result;
    }

    public static String createNext(String s) {
        if (s == null || "".equals(s)) {
            return "";
        }
        StringBuilder result = new StringBuilder();
        int num = 1;
        char c = s.charAt(0);
        for (int i = 1; i < s.length(); i++) {
            if (c == s.charAt(i)) {
                num++;
            } else {
                result.append(num);
                result.append(c);
                num = 1;
                c = s.charAt(i);
            }
        }
        result.append(num);
        result.append(c);
        return result.toString();
    }
}

参考解

https://leetcode-cn.com/problems/count-and-say/solution/

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