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

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++ 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; }

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