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I am trying to write an implementation on C# of Subsets pattern read here 14 Patterns to Ace Any Coding Interview Question:

It looks obvious but confuses me. My research says me it should be implemented via Jagged Arrays (not Multidimensional Arrays). I started:

I've got working code, but I'm looking to improve the way I understand and implement different coding techniques as a whole. I thought this problem presented a good chance to get feedback on what I'm doing.

The idea here is to take two arguments, an array and an integer. Identify all pairs in the array that sum to make the integer argument, and then return the sum of the indices. You cannot reuse an index, and you must always use the smallest index available to you. There is an explanation on the FCC code guide here: https://www.freecodecamp.org/learn/coding-interview-prep/algorithms/pairwise

So - here is the question. Is there any good way of doing this without using nested for loops? I am becoming increasingly aware of time/space complexities, and I know that O(n^2) won't land me the job. I would imagine a hashmap of some sort would come into it, but I just don't have the experience and knowledge to know how to use them.

Here is the code:

The Coding Question which I am trying to solve is this. I tried to solve but not all the test cases passed I am not able to find what could be the reason?

Identify possible words: Detective Bakshi while solving a case stumbled upon a letter which had many words whose one character was missing i.e. one character in the word was replaced by an underscore. For e.g.“Fi_er”. He also found thin strips of paper which had a group of words separated by colons, for e.g. “Fever:filer:Filter:Fixer:fiber:fibre:tailor:offer”. He could figure out that the word whose one character was missing was one of the possible words from the thin strips of paper. Detective Bakshi has approached you (a computer programmer) asking for help in identifying the possible words for each incomplete word.

You are expected to write a function to identify the set of possible words. The function identifyPossibleWords takes two strings as input where,

input1 contains the incomplete word, and input2 is the string containing a set of words separated by colons.

The function is expected to find all the possible words from input2 that can replace the incomplete word input1, and return the result in the format suggested below.

Example1 -

input1 = “Fi_er” input2 = “Fever:filer:Filter:Fixer:fiber:fibre:tailor:offer”

output string should be returned as “FILER:FIXER:FIBER” Note that –

The output string should contain the set of all possible words that can replace the incomplete word in input1 all words in the output string should be stored in UPPER-CASE all words in the output string should appear in the order in which they appeared in input2, i.e. in the above example we have FILER followed by FIXER followed by FIBER. While searching for input1 in input2, the case of the letters are ignored, i.e “Fi_er” matches with “filer” as well as “Fixer” as well as “fiber”. IMPORTANT: If none of the words in input2 are possible candidates to replace input1, the output string should contain the string “ERROR-009” Assumption(s):

Input1 will contain only a single word with only 1 character replaced by an underscore “_” Input2 will contain a series of words separated by colons and NO space character in between Input2 will NOT contain any other special character other than underscore and alphabetic characters.

My solution for the question is:

Trying to solve freecodecamp's symmetric difference challenge (https://www.freecodecamp.org/learn/coding-interview-prep/algorithms/find-the-symmetric-difference), I wrote the following function: