Return keypad code using recursion

Given the mobile numeric keypad. You can only press buttons that are up, left, right or down to the current button. You are not allowed to press bottom row corner buttons i. Given a number N, find out the number of possible numbers of given length. If we start with 0, valid numbers will be 00, 08 count: 2 If we start with 1, valid numbers will be 11, 12, 14 count: 3 If we start with 2, valid numbers will be 22, 21, 23,25 count: 4 If we start with 3, valid numbers will be 33, 32, 36 count: 3 If we start with 4, valid numbers will be 44,41,45,47 count: 4 If we start with 5, valid numbers will be 55,54,52,56,58 count: 5 ……………………………… ……………………………….

Keep doing this until N length number is obtained depth first traversal. Recursive Solution: Mobile Keypad is a rectangular grid of 4X3 4 rows and 3 columns Lets say Count i, j, N represents the count of N length numbers starting from position i, j. Following is the implementation of above recursive formula. Dynamic Programming There are many repeated traversal on smaller paths traversal for smaller N to find all possible longer paths traversal for bigger N. See following two diagrams for example.

return keypad code using recursion

Since the problem has both properties: Optimal Substructure and Overlapping Subproblemsit can be efficiently solved using dynamic programming. Following is the program for dynamic programming implementation. A Space Optimized Solution: The above dynamic programming approach also runs in O n time and requires O n auxiliary space, as only one for loop runs n times, other for loops runs for constant time. We can see that nth iteration needs data from n-1 th iteration only, so we need not keep the data from older iterations.

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We can have a space efficient dynamic programming approach with just two arrays of size Thanks to Nik for suggesting this solution. This article is contributed by Anurag Singh. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above. Writing code in comment? Please use ide. Length j. Lengths 0 and 1. Length k keypad[i,j]. Length k-1 from that new digit and. Add in count we found so far. Length "n". Write "Count for numbers of.

But it can always be written as DFS on 4X3 grid. But it can always be. A Space Optimized Python program to count. Return count of all possible numbers. Here we are explicitly writing lines for each number 0. Get count of all possible numbers of length "n" starting.

Driver program to test above function. This code is contributed by. Load Comments.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I do not want to use while or for loops, just want to use recursion to return the odd numbers in a given list.

Considering the default stack depth limit of in python, I would really not use recursion for this. I know there are a lot of recursive implementations above so here's a non-recursive one that is doing it the python way:.

And for the sake of completeness; if you really really must use recursion here's my go at it. This is very similar to the version by Josh Matthews. Here's another way of doing it which returns the list of odd numbers rather than modifying the list passed in.

It's written in emacs and inspired by gnibbler's answer. This one avoids the list copying overhead, at the cost of getting the answer backwards and a big increase in the ugliness factor:. Learn more. How can I return the odd numbers of a list, using only recursion in Python? Asked 9 years, 5 months ago. Active 7 years, 6 months ago. Viewed 19k times. I am not sure, why i got upvoted for my answer.

GlennMaynard sorry it came off as hw, as of 1 year ago [when this question was asked] I was in school studying a totally unrelated subject finance! I labaled it hw, because it was akin to questions asked in the hw section. Sorry it bothered you though. Active Oldest Votes. Josh Matthews Josh Matthews This is IMNSHO the best solution to date since it both minimises the arguments passed and doesn't damage the original list.

Can someone please explain in a little bit more detail how this program works? Btw when the list is too long then the program starts to spit out RuntimeError: maximum recursion depth exceeded in comparison. In this way, all of the elements in the list will be processed one at a time, and the resulting list will only contain the odd elements that were encountered.

It's the L[0:boolean] that's the stroke of gnenius John, whats not too like.It seems to be a real problem: we like solving real problems :p Given a digit string, return all possible letter combinations that the number could represent.

Note: Although the example above is in lexicographical order, the answer could however be in any order. This time we will try using Backtracking approach to solve this problem. Backtracking is a refinement of brute force approach and is in most cases a form of recursion, which systematically searches for a solution to a problem among all available options. If you need some further reading, you can read here.

Next step we go follow the orange path back to the parent-node and select the next child-node and so on and so forth until we passed by all the nodes of the tree. Here is the common solution in recursion :. But yet there is maybe a good news for those who also needs time to get with it — this problem can also be solved without using recursion, here is another solution:.

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This site uses Akismet to reduce spam. Learn how your comment data is processed. Like this: Like Loading Nice solution. Helped a lot to understand. Leave a Reply Cancel reply Enter your comment here Fill in your details below or click an icon to log in:. Email required Address never made public. Name required. Post to Cancel. By continuing to use this website, you agree to their use.

return keypad code using recursion

To find out more, including how to control cookies, see here: Cookie Policy.Below is a picture of such keypad. Given a keypad as shown in the diagram, and an n digit number, list all words which are possible by pressing these numbers. Approach: It can be observed that each digit can represent 3 to 4 different alphabets apart from 0 and 1. So the idea is to form a recursive function.

Then map the number with its string of probable alphabets, i. Now the recursive function will try all the alphabets, mapped to the current digit in alphabetic order and again call the recursive function for the next digit and will pass on the current output string.

Amazon Coding Interview Question - Recursive Staircase Problem

Implementation: Note that input number is represented as an array to simplify the code. This article is contributed by Jitendra Sangar. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above. Writing code in comment? Please use ide. The output words are one by one stored. It creates an output array and.

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A recursive function to print all. Try all 3 possible characters. A wrapper over printWordsUtil. This code is contributed by prajmsidc. Load Comments.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. Code Review Stack Exchange is a question and answer site for peer programmer code reviews. It only takes a minute to sign up. Your code is a reasonably neat use of recursion to solve the problem, and recursion is a good solution to this problem.

I prefer it for people to make it obvious that a function is used recursively to prepare myself for what to expect, I tend to use "recursive" in the name. A better solution would be to return a collection of results that you can print in a separate place. Personally I am not too concerned about the string-concatenation you use for computing the ans value when recursing, but there may be a better way with using a pre-computed array, with tracking indices.

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So, having said the above, it's best to explain it with code I would do two significantly different things I would set up a lookup table of string-based "digit" keys, and the corresponding character value. I would then loop through that table in the recursive function to determine the matches Setting up the table is relatively complicated, but it's a 1-time thing consisting of 2 correlated string arrays:.

Note that all the work is basically in the "string" space, and not parsing integers, etc. Rather than work with a String just work with characters when you can. Working with a String for the two characters is making use of the algorithm. For a single character? It's just the long way around.

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I prefer not to use intermediate variables for single uses, particularly if they don't have good names. I do like using intermediate variables e.

We do not need to handle the case when the parsed value is zero. The string is malformed in that case, so the value won't be correct.

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So we might as well not bother. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Print all possible codes for a given string Ask Question.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

Software Engineering Stack Exchange is a question and answer site for professionals, academics, and students working within the systems development life cycle. It only takes a minute to sign up. I just had a doubt in my mind. The following subroutine to search an element, in a list, for example has a return statement at the end:. I cannot get the significance of return statement at the end i.

C program to find GCD (HCF) of two numbers using recursion

It would be really helpful if anyone could explain this concept, using stack model. A return statement passes a value back to the immediate caller of the current function's call-frame.

In the case of recursion, this immediate caller can be another invocation of that same function. In most languages, if you don't use the return value of a function you called recursively or noteither that return value gets discarded or it is a diagnosable error. There are some languages where the return value of the last function call gets automatically re-used as the return value of the current function invocation, but they don't differentiate between normal and recursive function calls.

As soon as the function goes into the recursive call, you don't know what the result will be, because the result of the recursive call gets discarded.

Print All Possible Words from Phone Digits

Additionally, you promise to return a value from your function, but you have a path the recursive one where you don't specify what value to return. Depending on the language you use, this usually results either in a mandatory diagnostic or in undefined behaviour which is shorthand for: anything can happen and that can change at any time without notice. Don't hold anyone but yourself liable if it screws up your most important presentation.

There are some situations where the missing return value might appear to work, but that might change the next time you run the program with or without recompilation.

return keypad code using recursion

Two things; Returning the entire list in the case that you find the "x" you're looking for doesn't necessarily warrant using recursion, but that aside, consider the following:. January, February, You need the three returns for the possible outcomes.

The second, return l returns the list, in this case, letting you know you found your "x". The last is where the stack model comes into play.Question: Given a finite number, find out all the possible strings that can be generated by using encoding found on old telephone keypad.

Answer: This is a simple recursion problem. We should recurse the loop for each possible character of every digit in given number and append the character to the output. Code: Ruby code! PS: Follow-up to this question might be to remove duplicate in the output generated. Subscribe - To get an automatic feed of all future posts subscribe hereor to receive them via email go here and enter your email address in the box.

You can also like us on facebook and follow me on Twitter akashag Email This BlogThis! Share to Twitter Share to Facebook. I guess solution is already sorted and no duplication because no character is repeating for one number key and input char is also ordered. Let me know if I am not doing it right way.

Rahul: Why do you think that we need sorting in here for remove duplicity. There will not be any duplicate as per current logic and we don't need to take care for it. For clarity aab and baa are different. Please share your profile for the same at udayv amazon. Our challenge is to deliver the software systems which accurately capture, process, and report on the huge volume of financial transactions that are generated each day as millions of customers make purchases, as thousands of Vendors and Partners are paid, as inventory moves in and out of warehouses, as commissions are calculated, and as taxes are collected in hundreds of jurisdictions worldwide.

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