#0033

Binary Search

EasyDSA16 min10 XP

Problem

Given a sorted list nums and a target, return the target index if found. Return -1 otherwise.

Why This Matters

Binary search is the first algorithm where correctness depends on carefully maintained boundaries.

Function Signature

def binary_search(nums, target):

Examples

Example 1

Inputnums = [1, 3, 5, 7, 9], target = 7

Output3

The value 7 is at index 3.

Constraints

nums is sorted ascending.
Return -1 if target is missing.
Use O(log n) search.

CodePython

def binary_search(nums, target):
    """
    Input example: nums = [1, 3, 5, 7, 9], target = 7
    Return: 3
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    left = 0
    right = len(nums) - 1
    # write your code here
    return -1

def binary_search(nums, target):
    """
    Input example: nums = [1, 3, 5, 7, 9], target = 7
    Return: 3
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    left = 0
    right = len(nums) - 1
    # write your code here
    return -1

Visible browser tests run here when available.

Testcases2 visible / 4 hidden categories

Found target

Input[1, 3, 5, 7, 9], 7

Expected3

Binary search narrows until index 3 is found.

Missing target

Input[1, 3, 5, 7, 9], 4

Expected-1

The search range becomes empty.

Hidden Test Categories

Empty listSingle element foundSingle element missingTarget at first or last index