【python3】leetcode 34. Find First and Last Position of Element in Sorted Array（Medium）

momottyy

于 2019-01-20 21:19:16 发布

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本文介绍了一种在已排序整数数组中查找指定目标值起始和结束位置的有效算法，要求算法的时间复杂度为O(log n)。通过二分搜索策略，即使在大型数据集中也能快速定位目标元素的位置。

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

Given an array of integers nums sorted in ascending order, find the starting and ending position of a given target value.

Your algorithm's runtime complexity must be in the order of O(log n).

If the target is not found in the array, return [-1, -1].

Example 1:
Input: nums = [5,7,7,8,8,10], target = 8
Output: [3,4]
Example 2:
Input: nums = [5,7,7,8,8,10], target = 6
Output: [-1,-1]

class Solution:
    def searchRange(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        if target not in nums:return [-1,-1]
        low = nums.index(target)
        if nums.count(target) == 1:return [low,low]
        target += 1
        lo = low;hi = len(nums) -1
        while(lo <= hi):
            mid = (lo + hi) // 2     
            if nums[mid] >= target:hi = mid - 1
            else:lo = mid + 1
        return [low,hi]