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

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]

Code：

class Solution(object):
    def searchRange(self, arr, target):
        start = self.binary_search(arr, target-0.5)
        if not target in arr[start:start+1]:
            return [-1, -1]
        arr.append(0)
        end = self.binary_search(arr, target+0.5)-1
        return [start, end]

    def binary_search(self, arr, target):
        start, end = 0, len(arr)-1
        while start < end:
            mid = (start+end)//2
            if target < arr[mid]:
                end = mid
            else:
                start = mid+1
        return start