Binary_Search_leetcode.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
"""

class Solution:
    def search(self, nums: List[int], target: int) -> int:
        for i in range(len(nums)):
            if nums[i] == target:
                return i
        return -1
                       
# alternative solution: (2 pointer)

class Solution:
    def search(self, nums: List[int], target: int) -> int:
        N = len(nums)
        l,r = 0, N-1
        
        while l<=r:
            mid = (l+r)//2
            if nums[mid]==target:
                return mid
            elif nums[mid] < target:
                l = mid+1
            else:
                r = mid-1
        return -1