10-09 leeetcode 0034
链接 34. Find First and Last Position of Element in Sorted Array
题目
Given an array of integers nums sorted in non-decreasing order, find the starting and ending position of a given target value.
If target is not found in the array, return [-1, -1].
You must write an algorithm with O(log n) runtime complexity.
题解
二分查找到一个后，从中心向两边扩散，找到边界
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| class Solution:
def searchRange(self, nums: list[int], target: int) -> List[int]:
index = -1
if not nums:
return [-1, -1]
start, end = 0, len(nums) - 1
while start <= end:
mid = start + (end - start) // 2
if nums[mid] == target:
index = mid
break
elif nums[mid] > target:
end = mid - 1
else:
start = mid + 1
if index == -1:
return [-1, -1]
left, right = index, index
while (left >= 0 and nums[left] == target) or (
right < len(nums) and nums[right] == target
):
if left >= 0 and nums[left] == target:
left -= 1
if right < len(nums) and nums[right] == target:
right += 1
return [left + 1, right - 1]
|
