遞歸二進制搜索代碼中的StackOverflow錯誤

Question

我已經為“遞歸二進制搜索”編寫了此代碼。 我在標記的行得到了StackOverflowError 。 但是，我沒有使用(l+h)/2作為mid ，這可能會導致較大值的堆棧溢出。

public class RecursiveMethod
{
    public static int RecursiveBinarySearch(int[] array, int l, int h, int x)
    {
        l = 0;
        h = array.length - 1;

        while (l<=h)
        {
            int mid = l + (h-l)/2;

            if (x == array[mid])
                return mid;
            else if (x < array[mid])
                return RecursiveBinarySearch(array, l, mid-1, x); // overflow here
            else // last possibility: x > array[mid]
                return RecursiveBinarySearch(array, mid+1, h, x);
        }
        return -1;
    }

    public static void main (String[] args)
    {
        int[] a =
                  {2, 8, 12, 14, 16, 19, 24, 28, 31, 33,    // 0 - 9
                   39, 40, 45, 49, 51, 53, 54, 56, 57, 60,  // 10-19
                   63, 69, 77, 82, 88, 89, 94, 96, 97};     // 20-28

        for (int i = 0; i < a.length; i++)
            System.out.print("(" + a + "," + a[i] + ")" + "  ");

        System.out.println();
        System.out.print(RecursiveBinarySearch(a, 0, a.length, 1) + " ");
        System.out.print(RecursiveBinarySearch(a, 0, a.length, 26) + " ");
        System.out.print(RecursiveBinarySearch(a, 0, a.length, 85) + " ");
        System.out.print(RecursiveBinarySearch(a, 0, a.length, 99) + " ");
        System.out.println();
    }    
}

Answer 1

您始終設置l和h並忽略args。 因此，當您遞歸時，您又從精確的中間開始：

public static int RecursiveBinarySearch(int[] array, int l, int h, int x) {
  l = 0;
  h = array.length -1;

Answer 2

我不明白為什么在遞歸函數中使用while循環。 您應該按以下方式更改代碼，並且該代碼應該可以工作。

public class RecursiveMethod {
    public static int RecursiveBinarySearch(int[] array, int l, int h, int x) {
        if (h>=l)
            int mid = l + (h-l)/2;

        if (x == array[mid])
            return mid;
        else if ( l == h)
            return -1;
        else if (x < array[mid])
            return RecursiveBinarySearch(array, l, mid-1, x);
        if (x > array[mid])   // last possibility: x > array[mid]
            return RecursiveBinarySearch(array, mid+1, h, x);
    }
}

編輯正如布雷特·奧克肯（Brett Okken）所指出的那樣，您不應在通話中覆蓋您的l，h。