Generate all the strings of length n drawn from 0 ... k-1

Question

This problem is from the book Data Structure and Algorithms Made Easy by Narasimha Karumanchi chapter Recursion and Backtracking. The algorithm which is given in the book is as follows:

Let us assume we keep current k-ary string in an array A[0...n-1]. Call function k-string(n, k)

void k-string(int n, int k) {
  // process all k-ary strings of length m
  if(n < 1)
    printf("%s", A);       // Assume array A is a global variable
  else {
    for(int j=0; j<k; j++){
        A[n-1] = j;
        k-string(n-1, k);
    }
  } 
}

I couldn't understand the algorithm. Like why did they assigned an integer j to a string element?

I guess it's meant to illustrate the concept, not as working code. `A` is the string here, but not a character string, obviously, so `printf("%s"...` would not work. — 500 - Internal Server Error, May 11 '20 at 09:36
Yeah, I understand that it's a pseudo-code but I didn't understand `A[n-1] = j`. Why they did that? — Soumya Sharma, May 11 '20 at 10:41
That assignment is what builds the content of the string. Try stepping though e.g. with n==1 and k==3, or something. — 500 - Internal Server Error, May 11 '20 at 11:27
But j is an integer and it is going into a char array. How that will give a string in the final answer? — Soumya Sharma, May 11 '20 at 11:37
Right. That was the point of my previous comment: `A` is likely not a char array here but an array of int to make this assignment work. -- You could change A to `char[]` and then do something like `A[n-1] = (char) (j + 65);`, or whatever, to generate characters in the printable range, which would allow the `printf` to succeed. — 500 - Internal Server Error, May 11 '20 at 11:42

score 2 · Answer 1 · answered Jul 15 '20 at 06:10

package main

import "fmt"

func printResult(A []int, n int) {
    var i int
    for ; i < n; i++ {
        // Function to print the output
        fmt.Print(A[i])
    }
    fmt.Printf("\n")
}

// Function to generate all k-ary strings
func generateK_aryStrings(n int, A []int, i int, k int) {
    if i == n {
        printResult(A, n)
        return
    }
    for j := 0; j < k; j++ {
        // assign j at ith position and try for all other permutations for remaining positions
        A[i] = j
        generateK_aryStrings(n, A, i+1, k)
    }
}

func main() {
    var n int = 4
    A := make([]int, n)

    // Print all binary strings
    generateK_aryStrings(n, A, 0, 3)
    return
}

Generate all the strings of length n drawn from 0 ... k-1

1 Answers1