binarySearch.py

'''
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 <= 104
-104 < nums[i], target < 104
All the integers in nums are unique.
nums is sorted in ascending order.
'''

from typing import List

def search(self, nums: List[int], target: int) -> int:
    # two pointers approach:

    l, r = 0, len(nums)-1

    while l <= r:

        mid = (r + l) // 2 # or mid = l + (r - l)//2

        if nums[mid] < target:
            l = mid + 1
        elif nums[mid] > target:
            r = mid - 1
        else:
            return mid

    return -1