Day-17 Binary Search

Background

This problem statement is a part of LeetCode's learn card binary search. Under the sub-heading background.

Problem Statement

Given a sorted (in ascending order) integer array nums of n elements and a target value, 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

Note:

1. You may assume that all elements in nums are unique n will be in the range [1, 10000].
2. The value of each element in nums will be in the range [-9999, 9999].

Solution Approach

1. Keep dividing the array into halves.
2. left = 0, right = len(array)-1. Mid would be left+right/2.
3. Then determine where the element to be searched lies.

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

Learnings

1. Time complexity is O(logn).
2. Take care of the edge conditions.