0704-binary-search

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Description

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(Python)

class Solution:
    def search(self, nums: List[int], target: int) -> int:
        # arr[0] < arr[i] < arr[n-1]
        #   mid < target  l = mid + 1
        #   mid >= target r = mid
        #  -1 0 3 5 9 12
        #     5 < 9 l = 3 r =6
        l = 0
        r = len(nums) - 1
        if nums[l] == target:
            return l
        if nums[r] == target:
            return r
        while l < r:
            mid = (l + r) // 2
            if nums[mid] == target:
                return mid
            elif nums[mid] < target:
                l = mid + 1
            else:
                r = mid

        return -1

Dry Run