Two Sum solved in javascript

Two Sum : Javascript

Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

Code:

 var twoSum = function(nums, target) {
    //hash table
    var hash = {};

    for(let i=0; i<=nums.length; i++){
      //current number
        var currentNumber = nums[i];
        //difference in the target and current number
        var requiredNumber = target - currentNumber;
        // find the difference number from hashTable
        const index2 = hash[requiredNumber];

        // if number found, return index 
        // it will return undefined if not found
        if(index2 != undefined) {
            return [index2, i]
        } else {
           // if not number found, we add the number into the hashTable
            hash[currentNumber] = i;

        }
    }
};

In detail:

• Declare a empty hash table
• Loop through the array
• Store the current number in a variable
• Find the difference between the the target number and the current number
• Search for the difference number from the hash table
• If number found, return the index of the first number and the search number
• If not found, add the number into the hash table and continues for loop checking.

Conclusion:

Hashmap is the optimal solution as the average search time complexity is O(1)

Runtime	Memory
84 ms	35.5 MB

Comments

[Bhanu Chhabra]

This is O(N) complexity, not O(1)
There is for loop, and regardless of list construct, a non breaking for loop traversal is O(N).

[Abhishek Prakash]

I think he meant the time complexity of search operation on a hash table is O(1) and not for the solution.

[Bhanu Chhabra]

Well that is quite confusing. Atleast on my part it is.
People report the solution's complexity with subparts to prove some point.

But just pointing complexity of just 1 sub part and not talking about whole algo/solution is somewhat unusual.

[Bhanu Chhabra]

Also the conclusion doesn't matches with any content in description.

The base of conclusion should be discussed in opening statements.

[laith00x]

hey, can you please explain why in the return statement (return [index2, i]) you added 'i'? what is the value of i and how did it get the correct value? thanks in advance