Binary Search

Problem

https://leetcode.com/problems/binary-search/

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.

Example 1:

Input: nums = [-1,0,3,5,9,12], target = 9
Output: 4
Explanation: 9 exists in nums and its index is 4

Example 2:

Input: nums = [-1,0,3,5,9,12], target = 2
Output: -1
Explanation: 2 does not exist in nums so return -1

Constraints:

1 <= nums.length <= 10:sup:`4`
-10:sup:`4`< nums[i], target < 10:sup:`4`
All the integers in nums are unique.
nums is sorted in ascending order.

Pattern

Array, Binary Search

Approaches

Iterative

Code

def search(nums: list[int], target: int) -> int:
    """Search for ``target`` in sorted ``nums`` using binary search."""
    left = 0
    right = len(nums) - 1
    while left <= right:
        mid = (left + right) // 2
        if nums[mid] == target:
            return mid
        elif nums[mid] < target:
            left = mid + 1
        else:
            right = mid - 1
    return -1

Test

>>> from binary_search__iterative import search
>>> search([-1, 0, 3, 5, 9, 12], 9)
4
>>> search([-1, 0, 3, 5, 9, 12], 2)
-1

binary_search__iterative.search(nums: list[int], target: int) → int: Search for target in sorted nums using binary search.