Perhaps I should put some flesh on my comment:

There is only one way: understand your problem better. But that is as general as your question is

Your point is

Although I got my assumptions correct after some trial and error but I got too frustrated because of the lack of correct computing model in my head.

When I read trial and error, my alarm bells start ringing. Of course many of us know the state of mind, when one wants to fix a small problem and has wrapped his head around other things and starts guessing in one or the other way, to make the code seem to do, what is supposed to do. Some hackish solutions come out of this - and some of them are pure genius; but to be honest: most of them are not. Me included, knowing this state.

Independendly from your concrete problem, you asked questions, about how to improve:

1. Test =======

That was said by others and I would have nothing valuable to add

2. Problem Analysis ===================

It is hard to give some advice to that. There are only two hints I could give you, which probably help you improving your skills on that topic:

• the obvious and most trivial one is in the long term the most effective: solve many problems. While practicing and repeating you develop the mindset which helps you for future tasks. Programming is like any other activity to be improved by hard work practicing

Code Katas are a way, which might help a bit.

How do you get to be a great musician? It helps to know the theory, and to understand the mechanics of your instrument. It helps to have talent. But ultimately, greatness comes from practicing; applying the theory over and over again, using feedback to get better every time.

Code Kata

One site, which I like very much: Code Wars

Achieve mastery through challenge Improve your skills by training with others on real code challenges

They are relatively small problems, which help you sharpen your programming skills. And what I like most on Code Wars is, that you could compare your solution to one of others.

Or maybe, you should have a look at Exercism.io where you get feedback from the community.

• The other advice is nearly as trivial: Learn to break down problems You have to train yourself, breaking down problems into really small problems. If you say, you have problems in writing loops, you make the mistake, that you see the loop as a whole construct and do not deconstruct it into pieces. If you learn to take things apart step by step, you learn to avoid such mistakes.

I know - as I said above sometimes you are in such a state - that it is hard to break "simple" things into more "dead simple" tasks; but it helps a lot.

I remember, when I first learned professionally programming, I had huge problems with debugging my code. What was the problem? Hybris - The error can not be in such and such region of the code, because I know that it can not be. And in consequence? I skimmed through code instead of analyzing it I had to learn - even if it was tedious to break my code down instruction for instruction.

3. Develop a Toolbelt =====================

Besides knowing your language and your tools - I know these are the shiny things of which developers think first - learn Algorithms (aka reading).

Here are two books to start with:

• Introduction into algortihms

• Algorithms

This is like learning some recipes to start off cooking. At first you don't know what to do, so you have to look, what prior chefs cooked for you. The same goes for algortihms. Algorithms are like cooking recipies for common meals (data structures, sorting, hashing etc.) If you know them (at least try to) by heart, you have a good starting point.

3a) Know programming constructs

This point is a derivative - so to say. Know your language - and better: know, what constructs are possible in your language.

A common point for bad or inefficent code is sometimes, that the programmer does not know the difference between different types of loops (for-, while- and do-loops). They are somehow all interchangeably useable; but in some circumstances choosing another looping construct leads to more elegant code.

And there is Duff's device ...

P.S.:

otherwise your comment is no good than Donal Trump.

Yes, we should make coding great again!