Practice Problems - Two Sum

July 24, 20251 min read

Practice Problems - Two Sum

Problem Statement:

Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.

Pseudocode:

function twoSum(nums, target):
    hashmap = {}
    for i from 0 to length(nums) - 1:
        complement = target - nums[i]
        if complement in hashmap:
            return [hashmap[complement], i]
        hashmap[nums[i]] = i
    return []

Key Identifiers:

Array of integers
Target sum
Return indices of two numbers

Key Details Interviewers Look For:

Understanding of hash maps for O(n) solution
Handling edge cases (e.g., no solution)
Time and space complexity analysis

Implementations

Kotlin

    fun twoSum(nums: IntArray, target: Int): IntArray {
        val hashMap = MutableMap<Int, Int>()
        for ((i, num) in nums.withIndex()) {
            val complement = target - nums[i]
            if (hashMap.containsKey(compliment)) {
                return arrayOf(hashMap[compliment], i)
            }
            hashMap[nums[i]] = i
        }
        return arrayOf()
    }

Go

    func twoSum(nums []int, target int) []int {
        var hm = make(map[int]int)
        for k, num := range nums {
            complement := target - nums[k]

            if val, ok := hm[complement]; ok {
                return []int{val, k}
            }
            hm[num] = k
        }
        return nil
    }