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.
SOLUTION:
class Solution:
    def search(self, nums: List[int], target: int) -> int:
        n = len(nums)
        beg = 0
        end = n - 1
        while beg <= end:
            mid = (beg + end) // 2
            if nums[mid] == target:
                return mid
            elif beg == end:
                break
            elif nums[mid] > target:
                end = mid
            else:
                beg = mid + 1
        return -1

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