leetcode 每日一题 34. 在排序数组中查找元素的第一个和最后一个位置

二分法:

思路:

先用二分法找到左边界，再用二分法找到右边界。

class Solution:
    def searchRange(self, nums: List[int], target: int) -> List[int]:
        if not nums:
            return [-1,-1]
        def searchEdge(nums,target,isleft):
            l,r = 0,len(nums)
            while l<r:
                mid = (l+r)//2
                if nums[mid]>target or (isleft and nums[mid]==target):
                    r = mid
                else:
                    l = mid + 1
            return l
        leftIndex = searchEdge(nums,target,True)
        if leftIndex == len(nums) or nums[leftIndex]!=target:
            return [-1,-1]
        return [leftIndex,searchEdge(nums,target,False)-1]