[Leet Code] Binary Search

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

Problem:

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.

Solution:

class Solution(object):
    def search(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: int
        """
        high = len(nums)-1
        low = 0
        return self.binary_search(nums, target, high, low)
        
    def binary_search(self, nums, target, high, low):
        print("high", high)
        print("low", low)
        if high >= low:
            middle = (high + low) // 2
if target > nums[middle]:
                return self.binary_search(nums, target, high, middle+1)
            elif target < nums[middle]:
                return self.binary_search(nums, target, middle-1, low)
            else:
                return middle
        else:
            return -1