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

文章作者：Tyan
博客：noahsnail.com  |  CSDN  |  简书

1. Description

2. Solution

解析：最容易想到的就是二分查找，只是要进行一些修改，另一个方法是分别从前往后找以及从后往前找，满足条件就退出。

• Version 1

class Solution:
    def searchRange(self, nums, target):
        length = len(nums)
        start = -1
        end = -1
        left = 0
        right = length - 1

        while left <= right:
            mid = (left + right) // 2
            if nums[mid] > target:
                right = mid - 1
            elif nums[mid] < target:
                left = mid + 1
            else:
                if mid == 0 or nums[mid - 1] < target:
                    start = mid
                    break
                right = mid - 1

        left = 0
        right = length - 1
        while left <= right:
            mid = (left + right) // 2
            if nums[mid] > target:
                right = mid - 1
            elif nums[mid] < target:
                left = mid + 1
            else:
                if mid == length - 1 or nums[mid + 1] > target:
                    end = mid
                    break
                left = mid + 1

        return [start, end]

• Version 2

class Solution:
    def searchRange(self, nums, target):
        length = len(nums)
        start = -1
        end = -1
        for i in range(length):
            if nums[i] == target:
                start = i
                break
            if nums[i] > target:
                break

        if start == -1:
            return [start, end]

        for i in range(length -1 , -1, -1):
            if nums[i] == target:
                end = i
                break

            if nums[i] < target:
                break

        return [start, end]

Reference

1. https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array/