在升序整型数组中查找第一个大于等于目标值target的元素下标（左边界查找），下列实现正确的是？

第28594题单选题

已知升序整型数组nums，需实现查找第一个大于等于target的元素下标，若不存在则返回数组长度n。以下四个Python实现的二分查找代码片段，请问正确的是哪一个？

def left_bound(nums, target):
    left, right = 0, len(nums)-1
    while left < right:
        mid = (left + right) // 2
        if nums[mid] >= target:
            right = mid
        else:
            left = mid + 1
    return left

def left_bound(nums, target):
    left, right = 0, len(nums)-1
    while left <= right:
        mid = (left + right) // 2
        if nums[mid] >= target:
            left = mid + 1
        else:
            right = mid - 1
    return left

def left_bound(nums, target):
    left, right = 0, len(nums)-1
    while left <= right:
        mid = (left + right) // 2
        if nums[mid] >= target:
            right = mid - 1
        else:
            left = mid + 1
    return left

def left_bound(nums, target):
    left, right = 0, len(nums)-1
    while left <= right:
        mid = (left + right) // 2
        if nums[mid] > target:
            right = mid - 1
        else:
            left = mid + 1
    return left

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算法实现-二分边界条件处理

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