查找整数中相同数字的最长序列（Java）

Question

我需要编写一个递归方法，将int作为输入，并以int（而不是字符串）的形式返回其中最长的相同数字序列。计数序列并不是最难的部分，但当给定一个包含几个序列的数字时，我不知道如何返回正确的值，而不计算所有的序列，而只计算最长的序列。目前，我编写了一段只计算序列长度的代码：

public static int equalDigits (int num)
{
    return equalDigits(num, num % 10);
}

private static int equalDigits (int num, int last)
{
    if (num == 0)
        return 0;
    if (num % 10 == last)
    {
        last = num % 10;
        return 1 + equalDigits(num/10, last);
    }
    last = num % 10;
    return equalDigits(num/10, last);
}

我真的很难完成剩下的事情。

Answer 1

正如@markspace所说，通过上述代码无法识别最长的序列。代码需要记录从中间开始的可能的新序列，这意味着可能需要为目标变量和粘贴索引变量都有存储空间。

以下代码应能解决此问题：

import java.util.Scanner;

public class Sequence {

    public int countDigit(int input, int target, int height, int lastIndex, int count) {
        if (input != 0) {
            int currIndex = input % 10;

            if (lastIndex != currIndex) {
                // Checks if it is an index from a new starting sequence,
                // remove previous count, then count++.
                count = 0;
                count++;
            } else {
                // same sequence, then count++.
                count++;
            }
            
            // Below two lines for display purpose only.
            System.out.println("Count of target [" + target + "]: " + height);
            System.out.println("Count of currIndex [" + currIndex + "]: " + count);

            if (count > height) {
                // Checks if a new height in count is reached,
                // modify count.
                height = count;
                if (target != currIndex) {
                    // Checks if the new height is by a different index,
                    // modify target.
                    target = currIndex;
                }
            }

            lastIndex = currIndex;
            return countDigit(input / 10, target, height, lastIndex, count);
        } else {
            // if no input is left,
            return target;
        }
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int input = scanner.nextInt();

        Sequence sequence = new Sequence();

        System.out.println("Result: " + sequence.countDigit(input, 0, 0, 0, 0));

    }
}

输入为112999456，输出为：

Count of target [0]: 0
Count of currIndex [6]: 1
Count of target [6]: 1
Count of currIndex [5]: 1
Count of target [6]: 1
Count of currIndex [4]: 1
Count of target [6]: 1
Count of currIndex [9]: 1
Count of target [6]: 1
Count of currIndex [9]: 2
Count of target [9]: 2
Count of currIndex [9]: 3
Count of target [9]: 3
Count of currIndex [2]: 1
Count of target [9]: 3
Count of currIndex [1]: 1
Count of target [9]: 3
Count of currIndex [1]: 2
Result: 9

希望这个答案对你有帮助。