如何优化我的代码以最小化程序执行时间

Question

我正在尝试解决问题而且我编写了解决方案，但显然该程序运行时间太长。如何最大限度地减少它的运行时间？

这是我正在解决的问题：

Pebble Solitaire

这是我的代码：

import java.util.Scanner;

public class PebbleSolitaire {

    private static int maxDigits = 1 << 23;
    private static int[] posSol = new int[maxDigits];

    public static void main(String[] args) {
        Scanner reader = new Scanner(System.in);

        int cases = reader.nextInt();
        reader.nextLine();

        for (int caseCount = 0; caseCount < cases; caseCount++) {
            int lineInt = 0;
            String lineStr = reader.nextLine().trim();

            for (int i = 0; i < lineStr.length(); i++) {
                if (lineStr.charAt(i) == 'o') {
                    lineInt |= (1 << i);
                }
            }

            for (int i = 0; i < maxDigits; i++) {
                posSol[i] = -1;
            }

            System.out.println(calculateLeastPebbles(lineInt));
        }
    }

    private static int calculateLeastPebbles(int lineInt) {
        if (posSol[lineInt] != -1) {
            return posSol[lineInt];
        }

        int counter = 0;

        for (int i = 0; i < 23; i++) {
            if ((lineInt & (1 << i)) != 0) {
                counter++;
            }
        }

        for (int i = 0; i < 23; i++) {
            if (i >= 2 && ((lineInt ^ (3 << (i - 2))) & (7 << (i - 2))) == 0) {
                counter = Math.min(counter, calculateLeastPebbles(lineInt ^ (7 << (i - 2))));
            }
            if (i <= 20 && ((lineInt ^ (6 << i)) & (7 << i)) == 0) {
                counter = Math.min(counter, calculateLeastPebbles(lineInt ^ (7 << i)));
            }
        }

        return counter;
    }
}

我可以做些什么来加快速度？