instead of using target, using target-0.5 and target+0.5 as new target to find the low and up boundaries

```
class Solution(object):
def searchRange(self, nums, target):
"""
:type nums: List[int]
:type target: int
:rtype: List[int]
"""
l = self.search(nums, target-0.5)
r= self.search(nums, target+0.5)
if l == r:
return [-1, -1]
else:
return [l, r-1]
def search(self, nums, target):
l, r = 0, len(nums)
while l < r:
mid = (l+r)/2
if nums[mid] < target:
l = mid+1
else:
r = mid
return l
```