34. Find First and Last Position of Element in Sorted Array

#用二分查找法
class Solution(object):
    def searchRange(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        first = 0
        last = len(nums) - 1
        found = False
        
        results = [-1, -1]    
        if nums == []:
            return results
        if target < nums[0] or target > nums[last]:
            return results
        
        
        while first <= last and not found:
            mid = (first + last) // 2
            #找到了，分别继续向前，向后查找，直到找到第一个和最后一个target
            if target == nums[mid]:
                low = mid
                high = mid
                while low >= 0 and nums[low] == target:
                    low -= 1
                while high <= len(nums) - 1 and nums[high] == target: 
                    high += 1                
                found = True
            else:
                if target < nums[mid]:
                    last = mid - 1
                else:
                    first = mid + 1
        if found:            
            return [low+1, high-1]
        else:
            return results