Two-Sum: C#, Javascript, Python, Java

There are quite a few things that you can learn by solving one computer programming problem in various computer programming languages. So I decided to try out solving Two-Sum problem in 4 languages - C#, JavaScript, Python, and Java.

C# 

public int[] TwoSum(int[] nums, int target) {

        Dictionary<int, int> dict = new Dictionary<int, int>();

        for(int i=0; i < nums.Length; i++){

            int searchTerm = target-nums[i];

            if(dict.ContainsKey(searchTerm)){

                return new int[2] { dict[searchTerm], i};

            }else{

                dict.Add(nums[i], i);

            }

        }       

        return null;

    }

JavaScript

var twoSum = function(nums, target) {

    const map = {};

    for (let i = 0; i < nums.length; i++){

        let diff = target - nums[i];

        if(map[diff] !== undefined){

            return [map[diff], i];

        }else{

            map[nums[i]] = i;

        }

    }

    return null;

};

Python

def twoSum(self, nums: List[int], target: int) -> List[int]:

        map = {}

        for i, num in enumerate(nums) :

            diff = target - num

            if(map.get(diff) != None) :

                return [map[diff], i];

            else :

                map[num] = i;

        return None

Java

public int[] twoSum(int[] nums, int target) {

        Map<Integer, Integer> map = new HashMap<>();

        for (int i = 0; i < nums.length; i++) {

            int complement = target - nums[i];

            if (map.containsKey(complement)) {

                return new int[] { map.get(complement), i };

            }

            map.put(nums[i], i);

        }

        return null;

    }

Observations:

1. Code written in Python is probably the most succinct and readable one than the code written in other languages.

2. Coming from a C# background, it was refreshing to note that primary constructs like dictionary, loop, if-else is pretty much same across other programming languages with a difference in syntax. I did have to struggle to find equivalent of Dictionary in Java though. 

3. Python and JavaScript are similar in tone. Java and C# are similar in tone. There is a lot less ceremony in Python and JavaScript than what is required in Java and C#.

4. When I ran these solutions in LeetCode, the CPU time and memory consumption for each of the languages was a learning experience.

Memory footprint : Python's memory consumption is < 50% of what is typically consumed by Java, C# and JavaScript (perhaps running on Node.JS?). 

Runtime: Somehow Java turned out to be the fastest, I am not sure what compile time/run time optimization would cause this (something for me to learn more about). C# was the slowest by an order of magnitude, perhaps due to the extra time required to load assembly, JIT the code etc. Python was much faster than my expectations :).

All of the above observations can also be result of a transient issue on LeetCode servers. So, don't go by the performance numbers right away - better to run these on local machine and make up your mind.