June 5th 2023

Binary Search — Swift

Problem 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

Solution



class Solution {
    func search(_ nums: [Int], _ target: Int) -> Int {
        var start = 0
        var end = nums.count - 1

        while start <= end {
            var index = start + (end - start) / 2
            let value = nums[index]

            if (value == target){
                return index
            }else if (target > value){
                start = index + 1
            }else if (target < value){
                end = index  - 1
            }
        }

        return -1
    }
}

let s = Solution()

s.search([-1,0,3,5,9,12], 9)
s.search([5], 5)
s.search([2, 5], 5)

Discussion

It's WWDC week. Yay! It felt nice to work in Swift today.