Free Lisp to Check Missing and Repeating Number in Sequence



The creation of video games, artificial intelligence, and natural language processing have all made extensive use of a robust and adaptable programming language known as Lisp. 

Working with numerical sequences, or dealing with binary or burn tree are some of Lisp's main strengths, making it an excellent candidate because it effectively manipulates lists.


In this blog, we'll look at how to find missing and repeating numbers using a free Lisp dialect like SBCL or Clisp. 


Starting off with the method's fundamental theory as well as the crucial functions and variables from Lisp standard library. 


Then, moving on you will get to know a quick and effective technique that keeps track of the regularity of each value in the sequence using a hash table. This approach is easy to use, making it a suitable option for both novice and seasoned programmers.


But first let’s get a brief about free lisp.



What is Free Lisp?

The programming language Lisp has an open-source variant called Free Lisp. It is a free Lisp implementation that may be used for a variety of tasks, such as creating video games, artificial intelligence, and natural language processing.


 Due to its adaptability and simplicity, Free Lisp is frequently used to find burn tree, for AutoCAD commands etc. 


Although Free Lisp is no longer being actively developed, there are still various Open-Source Lisp implementations available, including SBCL, Clisp, ECL, and others. 


To understand it better, here’s an example of Free Lisp.



Example of Free Lisp

SBCL, a Common Lisp implementation, is a prime example of Free Lisp (Steel Bank Common Lisp). SBCL is a free and open-source Standard Lisp implementation that works with Windows, Macs, and Linux. It is renowned for its quick response times and effective memory management. 


Here is an instance of a straightforward SBCL program that computes a number's factorial:

(definitive factorial (n)


(In case (= n 0) 1 (* n ((factorial (1- n))))))


(output: 120) print (factorial 5)


Clisp, an open-source Standard Lisp implementation that works on a variety of platforms, is another illustration of Free Lisp.


Factorial (n) (defun) (if (eq n 0) 1 (* n ((factorial (1- n))))))


(output: 120) print (factorial 5)


The program in question is identical to the SBCL example but was created in Clisp. But you should also know about the methods and the necessary functions and macros from the Lisp standard library. 


So, in the next phase we have discussed it in detail!



Methods, necessary functions and macros from the Lisp standard library

A hash table is used to keep track of the occurrence of each value in the sequence when utilising a free Lisp language like SBCL or Clisp to find missing and repeating numbers in a sequence.


The fundamental concept is to iterate through the list of numbers, adding each value within the hash table while keeping track of the number of times the number appears. 


By looping through the sequence once more, you can look up at each value within the hash table to see if it repeats or is missing. A number that is missing indicates that it has not been included to the hash table, while a number that repeats indicates that it has been included within the hash table more than once.


The following Lisp standard library functions and macros are used in this approach:


  • make-hash-table: Use the make-hash-table function to build a fresh hash table. It accepts a number of optional keyword parameters, such as test, that is used to provide the hash table's equality test method.

  • loop: This macro is utilised to repeatedly iterate through the list of numbers.

  • gethash: gethash is a function that searches a hash table for a value. It accepts the hash table and the value's key as arguments.

  • setf: Set a key's value in a hash table using the setf function.

  • equal: This function determines whether two values are equal.

  • format: The string is formatted using this function, which takes nil as its first argument to utilise the default output (usually standard-output).

  • Length: The sequence's length is returned by this function from the argument it has been given.


You can quickly find missing and repeating values in a sequence using these macros and functions in Lisp. These operations are crucial components of Lisp standard library because they offer a strong and adaptable toolkit for addressing a variety of issues.



Free Lisp to Check Missing and Repeating Number in Sequence

Here is an instance of a Common Lisp program that checks a sequence of numbers for missing and repeated numbers using a hash table:


This program accepts a set of values as input and keeps track of the occurrence of each value in the series using a hash table. It then runs over the sequence, searching up each number in the hash table to find missing and repeating values. 


The program gives the value of "Missing number: [number]" in the case of missing numbers and the "Repeating number: [number]" as output in the case of repeating numbers.


This function can be used with a set of values by calling it and passing the sequence as an input, as in the following example:


(check-missing-repeating '(4 9 8 7 8 5))


Then the output will be:


Missing number: 6

Repeating number: 8


  • This program makes use of the Standard Lisp standard library's loop macro and make-hash-table function.

  • Additionally, it makes use of the gethash and setf functions to look up and set the values of values in hash tables, respectively.

  • It also employs the equal test function, which evaluates the equality of two numbers.

  • Additionally, the format function is used to format the string, and the standard output stream is used by using nil as the first parameter (usually standard-output).

  • To determine the sequence's length, it also makes use of the length function.



Conclusion

Hope you now have a firm grasp on how to use Lisp to find missing and repeating  numbers in a sequence and that you have the skills necessary to solve other problems of a similar nature in the future.


The strength of Lisp resides in its capacity to handle sophisticated operations and complicated data structures with efficiency, making it an excellent solution for a variety of issues.

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