Recursively print all sentences that can be formed from list of word lists

3

Given a list of word lists How to print all sentences possible taking one word from a list at a time via recursion?

Example:

Input: {{"you", "we"},
        {"have", "are"},
        {"sleep", "eat", "drink"}}

Output:
  you have sleep
  you have eat
  you have drink
  you are sleep
  you are eat
  you are drink
  we have sleep
  we have eat
  we have drink
  we are sleep
  we are eat
  we are drink 

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The idea is based on simple depth first traversal. We start from every word of first list as first word of an output sentence, then recur for the remaining lists.

Below is C++ implementation of above idea. In the below implementation, input list of list is considered as a 2D array. If we take a closer look, we can observe that the code is very close to DFS of graph.

C++

// C++ program to print all possible sentences from a list of word list
#include <iostream>
#include <string>

#define R 3
#define C 3
using namespace std;

// A recursive function to print all possible sentences that can be formed
// from a list of word list
void printUtil(string arr[R][C], int m, int n, string output[R])
{
    // Add current word to output array
    output[m] = arr[m][n];

    // If this is last word of current output sentence, then print
    // the output sentence
    if (m==R-1)
    {
        for (int i=0; i<R; i++)
           cout << output[i] << " ";
        cout << endl;
        return;
    }

    // Recur for next row
    for (int i=0; i<C; i++)
       if (arr[m+1][i] != "")
          printUtil(arr, m+1, i, output);
}

// A wrapper over printUtil()
void print(string arr[R][C])
{
   // Create an array to store sentence
   string output[R];

   // Consider all words for first row as starting points and
   // print all sentences
   for (int i=0; i<C; i++)
     if (arr[0][i] != "")
        printUtil(arr, 0, i, output);
}

// Driver program to test above functions
int main()
{
   string arr[R][C]  = {{"you", "we"},
                        {"have", "are"},
                        {"sleep", "eat", "drink"}};

   print(arr);

   return 0;
}

Python

# Python program recursively print all sentences that can be
# formed from list of word lists
R = 3
C = 3

# A recursive function to print all possible sentences that can
# be formed from a list of word list
def printUtil(arr, m, n, output):

    # Add current word to output array
    output[m] = arr[m][n]

    # If this is last word of current output sentence, then print
    # the output sentence
    if m==R-1:
        for i in xrange(R):
            print output[i] + " ",
        print "\n",
        return

    # Recur for next row
    for i in xrange(C):
        if arr[m+1][i] != "":
            printUtil(arr, m+1, i, output)

# A wrapper over printUtil
def printf(arr):

    # Create an array to store sentence
    output = [""] * R

    # Consider all words for first row as starting
    #  points and print all sentences
    for i in xrange(C):
        if arr[0][i] != "":
            printUtil(arr, 0, i, output)

# Driver program
arr = [ ["you", "we",""],
        ["have", "are",""],
        ["sleep", "eat", "drink"]]
printf(arr)
# This code is contributed by Bhavya Jain


Output:
  you have sleep
  you have eat
  you have drink
  you are sleep
  you are eat
  you are drink
  we have sleep
  we have eat
  we have drink
  we are sleep
  we are eat
  we are drink 

This article is contributed by Kartik. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above

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