在排序数组中查找元素的第一个和最后一个位置

#python 
class Solution:
    def searchRange(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        left = 0 
        right = len(nums)-1
        while left<=right:
            mid = (left+right)//2
            if target<nums[mid]: right=mid-1
            elif target>nums[mid]:left=mid+1
            else:
                left = mid
                right = mid
                while(left>=0 and nums[left]==target):left-=1
                while(right<=len(nums)-1 and nums[right]==target):right+=1
                return [left+1,right-1]
        return [-1,-1]