704. 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</sup>

• -10<sup>4</sup> < nums[i], target < 10<sup>4</sup>

• All the integers in nums are unique.

• nums is sorted in ascending order.

Solution:

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

        while l <= r:
            m = l + ((r - l) // 2)  # (l + r) // 2 can lead to overflow
            if nums[m] > target:
                r = m - 1
            elif nums[m] < target:
                l = m + 1
            else:
                return m
        return -1