Question

我正在做一个使用分治法的程序。不幸的是，我不能使用find(...)方法。我不知道该怎么办，而不是在这一行：find(null, 0, 100, 34)中返回null。预先谢谢你。

public class Main {
    static int find (double T[], int left, int right, double numToSearch) {
        if (left <= right) {
            int middle = (left + right) / 2;
            if (T[middle] == numToSearch) {
                return middle;
            }
            if (T[middle] < numToSearch) {
                return find(T, middle+1, right, numToSearch);
            }
            return find(T, left, middle-1, numToSearch);
        }
        return -1;      
    }

    public static void main(String[] args) {
        System.out.println(find(null /* (OR WHAT HERE TO MAKE IT WORK) */, 0, 100, 34));
    }

Answer 1

您必须提供一个数组，double[]。另外，您必须使用该数组作为第一个参数和有效的第三个参数（“ right”不得大于数组的最大索引）来调用find(...)方法。

请参见以下代码，该代码基本上是您的代码以及示例数组，对find方法的正确调用以及main方法中的一些（希望是有帮助的）注释：

public class Main {

    static int find(double T[], int left, int right, double numToSearch) {
        if (left <= right) {
            int middle = (left + right) / 2;
            if (T[middle] == numToSearch) {
                return middle;
            }
            if (T[middle] < numToSearch) {
                return find(T, middle + 1, right, numToSearch);
            }
            return find(T, left, middle - 1, numToSearch);
        }
        return -1;
    }

    public static void main(String[] args) {
        // create an array that you can use for searching a number, here it is 34 at index 8
        double[] array = {1, 2, 3, 4, 5, 6, 7, 30, 34, 44, 45, 66, 67, 71, 72, 73, 77, 85, 89, 90, 99};
        // use the find-method with a valid maximum index (right) and the array defined before
        System.out.println(find(array, 0, array.length - 1, 34));
    }

}

结果仅为8，所以可能在输出中添加更多信息，如下所示：

public static void main(String[] args) {
    // create an array that you can use for searching a number, here it is 34 at index 8
    double[] array = {1, 2, 3, 4, 5, 6, 7, 30, 34, 44, 45, 66, 67, 71, 72, 73, 77, 85, 89, 90, 99};
    double numberToFind = 34;
    // use the find-method with a valid maximum index (right) and the array defined before
    System.out.println("The number " + numberToFind + " is at index " + find(array, 0, array.length - 1, 34));
}

分而治之算法-结果NullPointerException

1 个答案: