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

code by python:

class Solution:
    def search(self, nums: List[int], target: int) -> int:
        def bs(start, end):
            # base condition
            if start > end:
                return -1

            mid = (start + end) // 2

            if nums[mid] < target:
                return bs(mid + 1, end)
            elif nums[mid] > target:
                return bs(start, mid - 1)
            else:
                return mid
        return bs(0, len(nums) - 1)