Date: February 02, 2026
Category: Arrays | Binary Search
Time Taken: 15 minutes
Difficulty: Easy

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Problem Statement

Given an array of integers nums which is sorted in ascending order, and an integer target, write a function to search target in nums. If target exists, then return its index. Otherwise, return -1.

You must write an algorithm with O(log n) runtime complexity.

Link: Binary Search

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Solution 1 (HashMap):

• We could use a HashMap to associate each value with its index.

• Then, we can check if the target is in the HashMap. If it is, we return the index; if not, we return -1.

• This solution is not Not O(logN).

Solution Code

class Solution:
    def search(self, nums: List[int], target: int) -> int:
        seen = {}
        for index, value in enumerate(nums):
            seen[value] = index

        if target in seen:
            return seen[target]
        return -1

Complexity:

Time: O(N) Space: O(N)

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Solution 2 (Binary Search) [Optimized]:

• The proper solution is to write a Binary Search algorithm. We will start with two pointers: left and right.

• While left <= right, we will define a variable middle as left + (right - left) // 2. We use // instead of / to ensure we get whole numbers, not decimals.

• If the target is smaller than middle, we will move right to middle - 1. If the target is larger than middle, we will move left to middle + 1. If neither is true, it means middle equals the target, and we will return the middle index.

Solution Code (No separate arrays)

class Solution:
    def search(self, nums: List[int], target: int) -> int:
        left = 0
        right = len(nums) - 1

        while left <= right:
            middle = left + (right - left) // 2
            if target > nums[middle]:
                left = middle + 1
            elif target < nums[middle]:
                right = middle - 1
            else:
                return middle
        return -1

Complexity:

Time: O(logN) Space: O(1)

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Key Takeaway: How Binary Search in written in Python.

Pattern: Binary Search

Series: 90 Days of Data Engineering Progress: 29/90 problems completed

Tags: #DEQuest #LeetCode #Python #DataEngineering #BuildInPublic