Two Sum II - Two Pointers Algorithm - Leetcode 167

FAANG Coding Interviews / Data Structures and Algorithms / Leetcode

[GregHogg]

Master Data Structures & Algorithms For FREE at AlgoMap.io!

[RS-fzps]

This is a great teaching question. I love it when an answer has a (more or less) optimal solution that uses two pointers.

[md.shariarkabir]

Binary search or Two Pointer : TC => O(nlogn) SC => O(1) (When Array not sorted)
TC => O(n) SC => O(1) (sorted array)
Hash Map: TC => O(n), SC => O(n)

[not_vinkami]

I saw you using n as in r = n - 1 before declaring that n = len(numbers)
Good job

[kareems]

finally someone who can explain two pointer simply

[VanisreeSunkara]

So the reason we used two point here is becoz this is sorted right? Not in two sum 1 as it wasn't sorted?!

[hakan]

Would be great if you displayed the time complexity in the end

[pablourbanohernandezvizcarra]

Great video, please continue with this short videos solving algorithms are very useful.

[monish.v]

Is any chance using two pointer it may miss any element to check ? or it's time complexity may be high ?

[Progamertoat]

How does your code work if you declarated r before n if the declaration of r is dependent of n?

[themrunknown]

Quick question, does it work if you just have a dictionary(hashmap)? Like index through each of the element A[i] then store (target - A[i]) as the key and its index as the value. Then return the index if found in the hashmap. This is O(n) too I believe.
P/s: if it need constant space then 2 pointer is the way to go.

[CTT]

if only two numbers, then extremely simple. In general, suppose we want to look for numbers, no matter how many, that have the summation equal to a given number k, then a fundamental way is to apply dynamic programming.

[elochess]

i would just do like put p1 on 0 then p2 from 1-len of list then if sum not found, p1 goes to 1 and p2 starts from 2-len of list, this continues until sum is found

then if p1 == p2: return p1, p2

works on both two sum and two sum II

[P.Shivakrishna]

It looks like a binary search what is difference between the br and tp

[learnwithbharath-]

Anyone know greg using which tool explain problem like white borad

[giantbush]

Suggestion: Pls pause for an extra couple of seconds after revealing your soln.

[shrayesraman]

Do these companies still ask such easy questions?

[SSIRP]

It doesn't work for negative numbers or target.

[BederikStorm]

Three sum is more interesting.
You have a loop of index i and inside you solve with this TP algorithm to find j and k

[tellmewhyaintnothinbutaheartac]

could you still use a hash map on this one?