给出折半查找的递归和非递归算法

折半查找也叫二分查找，是一种在有序数组中查找特定元素的搜索算法。以下是折半查找的递归和非递归版本：

**递归算法（Python）：**

def binary_search_recursive(arr, target, low, high):
    if low <= high:
        mid = (low + high) // 2
        if arr[mid] == target:
            return mid
        elif arr[mid] < target:
            return binary_search_recursive(arr, target, mid + 1, high)
        else:
            return binary_search_recursive(arr, target, low, mid - 1)
    else:
        return -1  # 如果目标不在数组中，返回-1

# 使用方法
arr = [1, 3, 5, 7, 9]
target = 5
result = binary_search_recursive(arr, target, 0, len(arr) - 1)

**非递归算法（Python）：**

def binary_search_iterative(arr, target):
    low = 0
    high = len(arr) - 1
    
    while low <= high:
        mid = (low + high) // 2
        if arr[mid] == target:
            return mid
        elif arr[mid] < target:
            low = mid + 1
        else:
            high = mid - 1
            
    return -1  # 目标未找到

# 使用方法
arr = [1, 3, 5, 7, 9]
target = 5
result = binary_search_iterative(arr, target)