Print a sorted list of words represented by the expression under the given grammar

In this article, we will be exploring an interesting problem related to expressions and grammar in C++. The problem statement is "Print a sorted list of words represented by the expression under the given grammar". This problem offers a great opportunity to brush up your knowledge on parsing expressions, handling strings, and sorting algorithms in C++.

Problem Statement

Given a string expression where each character represents a lowercase English letter and the '|' character represents an OR operation, the task is to print a sorted list of all possible words represented by the expression.

C++ Solution Approach

Our approach to solve this problem is by using recursion to parse the expression and generate all possible words. We'll also use a set data structure to store the words and maintain them in sorted order.


Here's the C++ code that implements this solution −

#include <iostream>
#include <set>
#include <string>
using namespace std;

void generateWords(string expr, string word, set<string>& words) {
   if (expr.empty()) {
   string temp = word;
   for (int i = 0; i < expr.size(); i++) {
      if (expr[i] == '|') {
            generateWords(expr.substr(i + 1), word, words);
            word = temp;
      } else {

void printWords(string expr) {
   set<string> words;
   generateWords(expr, "", words);
   for (const string& word : words) {
      cout << word << endl;

int main() {
   string expr = "a|b|c";
   cout << "The sorted list of words is: " << endl;
   return 0;


The sorted list of words is: 

Explanation with a Test Case

Let's consider the expression "a|b|c".

When we pass this expression to the printWords function, it generates all possible words represented by the expression and stores them in a set to maintain them in sorted order.

The possible words are "abc" (combining all characters), "ac" (removing 'b'), "bc" (removing 'a'), and "c" (removing 'a' and 'b').

The function then prints the sorted list of words, which is "abc", "ac", "bc", "c".

So, the output you're getting is indeed correct according to the given code and problem statement. I apologize for the earlier confusion.


This problem provides a great opportunity to practice parsing expressions and generating sequences using recursion in C++. It's an excellent problem to practice your C++ coding skills and to understand how to use recursion and set data structures for problem-solving.

Updated on: 18-May-2023


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