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C++ program to print unique words in a file

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  • Difficulty Level : Medium
  • Last Updated : 07 Aug, 2022
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Write a function that takes a file name as argument and prints all unique words in it. We strongly recommend you to minimize your browser and try this yourself first The idea is to use map in STL to keep track of words already occurred. 


// C++ program to print unique words in a string
#include <bits/stdc++.h>
using namespace std;
// Prints unique words in a file
void printUniquedWords(char filename[])
    // Open a file stream
    fstream fs(filename);
    // Create a map to store count of all words
    map<string, int> mp;
    // Keep reading words while there are words to read
    string word;
    while (fs >> word)
        // If this is first occurrence of word
        if (!mp.count(word))
            mp.insert(make_pair(word, 1));
    // Traverse map and print all words whose count
    //is 1
    for (map<string, int> :: iterator p = mp.begin();
        p != mp.end(); p++)
        if (p->second == 1)
            cout << p->first << endl;
// Driver program
int main()
    // Create a file for testing and write something in it
    char filename[] = "test.txt";
    ofstream fs(filename, ios::trunc);
    fs << "geeks for geeks quiz code geeks practice for qa";
    return 0;



Time complexity: O(nlogn) where n is no of words in given file

Auxiliary Space: O(n)

Thanks to Utkarsh for suggesting above code. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above

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