def binary_search(arr, target):
    """
    二分查找算法
    返回目标值在数组中的索引，如果不存在则返回 -1
    """
    left, right = 0, len(arr) - 1

    while left <= right:
        mid = left + (right - left) // 2  # 防止溢出

        if arr[mid] == target:
            return mid
        elif arr[mid] < target:
            left = mid + 1
        else:
            right = mid - 1

    return -1


def test_binary_search():
    """测试二分查找函数"""
    test_cases = [
        # (数组, 目标值, 期望索引)
        ([1, 2, 3, 4, 5], 3, 2),
        ([1, 2, 3, 4, 5], 1, 0),
        ([1, 2, 3, 4, 5], 5, 4),
        ([1, 2, 3, 4, 5], 0, -1),
        ([1, 2, 3, 4, 5], 6, -1),
        ([], 5, -1),
        ([5], 5, 0),
        ([5], 3, -1),
        ([1, 3, 5, 7, 9], 7, 3),
        ([1, 3, 5, 7, 9], 2, -1),
    ]

    all_passed = True
    for i, (arr, target, expected) in enumerate(test_cases):
        result = binary_search(arr, target)
        if result == expected:
            print(f"测试用例 {i + 1} 通过: binary_search({arr}, {target}) = {result}")
        else:
            print(f"测试用例 {i + 1} 失败: binary_search({arr}, {target}) = {result}, 期望 {expected}")
            all_passed = False

    if all_passed:
        print("所有测试用例通过!")
    else:
        print("部分测试用例失败!")

    return all_passed


if __name__ == "__main__":
    # 运行测试
    test_binary_search()