use binary search, find the first number that biger or equal to the target

```
class Solution(object):
def searchInsert(self, nums, target):
"""
:type nums: List[int]
:type target: int
:rtype: int
"""
if not nums:
return 0
if target > nums[len(nums) - 1]:
return len(nums)
left = 0
right = len(nums) - 1
while left < right:
mid = left + (right - left)/2
if nums[mid] < target:
left = mid + 1
else:
right = mid
return left
```