以下哪个代码片段可以正确实现升序整数数组的左边界查找（即找到第一个大于等于目标值target的元素下标，若所有元素均小于target则返回数组长度n）？

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

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

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

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