LeetCode 704. Binary Search

Description

https://leetcode.com/problems/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.

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
  • -9999 <= nums[i], target <= 9999
  • All the integers in nums are unique.
  • nums is sorted in an ascending order.

Explanation

Just implement a basic binary search to search for the target.

Python Solution

class Solution:
    def search(self, nums: List[int], target: int) -> int:
        
        
        start = 0
        end = len(nums) - 1
        
        while start + 1 < end:
            
            mid = start + (end - start) // 2
            
            if nums[mid] == target:
                return mid
            elif nums[mid] > target:
                end = mid
            else:
                start = mid
                
        if nums[end] == target:
            return end
        elif nums[start] == target:
            return start
        
        return -1
  • Time Complexity: O(log(N)).
  • Space Complexity: O(1).

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