LeetCode_Find First and Last Position of Element in Sorted Array

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].

（在时间复杂度为O(log n)的前提下在有序数组中检索target的第一次及最后一次）

Example:

1. 二分查找

class Solution:
    def searchRange(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        
        n = len(nums)
        if n == 0:
            return [-1, -1]
        
        re_left, re_right = -1, -1

        # find the first index
        left, right = 0, n-1
        while left <= right:
            middle = (left + right) // 2
            
            if target == nums[middle]:
                re_left = middle
                right = middle - 1
            elif target > nums[middle]:
                left = middle + 1
            else:
                right = middle - 1
        
        if nums[left] != target:
        	return [-1, -1]
           
        # find the last index     
        left, right = 0, n-1 
        while left <= right:
            middle = (left + right) // 2
            
            if target == nums[middle]:
                re_right = middle
                left = middle + 1
            elif target > nums[middle]:
                left = middle + 1
            else:
                right = middle - 1
                
        return [re_left, re_right]