给定一个有序序列，使用二分查找指定的值。（递归/非递归两种方法）

非递归方法：

def binary_search(arr, target):
    left = 0
    right = len(arr) - 1

    while left <= right:
        mid = (left + right) // 2
        if arr[mid] == target:
            return mid
        elif arr[mid] < target:
            left = mid + 1
        else:
            right = mid - 1

    return -1

递归方法：

def binary_search_recursive(arr, target, left, right):
    if left > right:
        return -1

    mid = (left + right) // 2
    if arr[mid] == target:
        return mid
    elif arr[mid] < target:
        return binary_search_recursive(arr, target, mid + 1, right)
    else:
        return binary_search_recursive(arr, target, left, mid - 1)

调用方法：

arr = [1, 3, 5, 7, 9]
target = 5

# 调用非递归方法
result = binary_search(arr, target)
print(result)

# 调用递归方法
result = binary_search_recursive(arr, target, 0, len(arr) - 1)
print(result)

输出：

2
2