題目：用遞迴和非遞迴兩種方法實現二分查詢

非遞迴法：

int binary_search(int *arr, int lenth, int key)
{
    assert(arr != NULL);
    int left = 0;
    int right = lenth - 1;
    int mid = 0;

    while (left <= right)
    {
        mid = left + ((right - left) >> 1);//效率高且沒有溢位問題
        if (key > arr[mid])
        {
            left = mid + 1
 
;
        }
        else if (key < arr[mid])
        {
            right = mid - 1;
        }
        else
        {
            return mid;
        }
    }
    return -1;//找不到返回-1
}

void test()//測試部分
{
    int arr[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
    int lenth = sizeof(arr) / sizeof(arr[0]);

    printf
 
("%d\n", binary_search(arr, lenth, 0));
    printf("%d\n", binary_search(arr, lenth, 1));
    printf("%d\n", binary_search(arr, lenth, 2));
    printf("%d\n", binary_search(arr, lenth, 3));
    printf("%d\n", binary_search(arr, lenth, 4));
    printf("%d\n", binary_search(arr, lenth, 5));
    printf("%d
 
\n", binary_search(arr, lenth, 6));
    printf("%d\n", binary_search(arr, lenth, 7));
    printf("%d\n", binary_search(arr, lenth, 8));
    printf("%d\n", binary_search(arr, lenth, 9));
    printf("%d\n", binary_search(arr, lenth, 10));
}
int main()
{
    test();
    system("pause");
    return 0;
}

測試結果：

遞迴法：

int binary_search(int *arr, int left, int right, int key)
{
    assert(arr != NULL);

    if (left <= right)
    {
        int mid = left + ((right - left) >> 1);
        if (key > arr[mid])
        {
            return binary_search(arr, mid+1, right, key);
        }
        else if (key < arr[mid])
        {
            return binary_search(arr, left, mid-1, key);
        }
        else
        {
            return mid;
        }
    }
    else
    {
        return -1;
    }
}

void test()
{
    int arr[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
    int lenth = sizeof(arr) / sizeof(arr[0]);

    printf("%d\n", binary_search(arr, 0, 9, 0));
    printf("%d\n", binary_search(arr, 0, 9, 1));
    printf("%d\n", binary_search(arr, 0, 9, 2));
    printf("%d\n", binary_search(arr, 0, 9, 3));
    printf("%d\n", binary_search(arr, 0, 9, 4));
    printf("%d\n", binary_search(arr, 0, 9, 5));
    printf("%d\n", binary_search(arr, 0, 9, 6));
    printf("%d\n", binary_search(arr, 0, 9, 7));
    printf("%d\n", binary_search(arr, 0, 9, 8));
    printf("%d\n", binary_search(arr, 0, 9, 9));
    printf("%d\n", binary_search(arr, 0, 9, 10));
}
int main()
{
    test();
    system("pause");
    return 0;
}

測試結果：