Find and print duplicate words in std::vector<string> using STL functions - GeeksforGeeks

25 Nov, 2020
Consider an array of string and find duplicate words in that array and print that duplicate words if exist.Examples:  
Input : { "welcome", "to", "geeks", "for", "geeks" }
Output : geeks

Input : { "reduce", "reuse", "recycle", "reduce", 
          "reuse", "recycle", " recycle" }
Output : recycle
reduce
reuse

Input : { "Go", "Green" }
Output : No Duplicate words
 
Method 1 (Using Sorting) 1. Sort array of string. 2. compare adjacent word in array of string. 3. if two word are same then push that word in another vector string. 4. print the duplicate words if exist. 
CPP
// CPP program to find duplicate word in a// vector<string>#include <bits/stdc++.h>using namespace std; void printDuplicates(vector<string> words){    vector<string> duplicate;     // STL function to sort the array of string    sort(words.begin(), words.end());     for (int i = 1; i < words.size(); i++) {        if (words[i - 1] == words[i]) {             // STL function to push the duplicate            // words in a new vector string            if (duplicate.empty())              duplicate.push_back(words[i]);            else if (words[i] != duplicate.back())                duplicate.push_back(words[i]);        }    }     if (duplicate.size() == 0)        cout << "No Duplicate words" << endl;    else        for (int i = 0; i < duplicate.size(); i++)            cout << duplicate[i] << endl;} // Driver codeint main(){    vector<string> words{ "welcome", "to", "geeks", "for",                          "geeks",   "to", "geeks" };    printDuplicates(words);    return 0;}
geeks
to

 Method 2 (Using Hashing) 1. Create an empty hash table. 2. One by one traverse words. 3. For every word check if already exists in the hash. ........if (already exists in hash) .............Print the word ........Else .............Insert the word in hash. 
CPP
// CPP program to find duplicate word in a// vector<string>#include<bits/stdc++.h>using namespace std; void printDuplicates(vector<string> words){    unordered_set<string> s;     bool dupFound = false;    for (int i = 1; i<words.size(); i++)    {        if (s.find(words[i]) != s.end())        {            cout << words[i] << endl;            dupFound = true;        }        else            s.insert(words[i]);    }     if (dupFound == false)        cout << "No Duplicate words" << endl;} // Driver codeint main(){    vector<string>words{ "welcome", "to", "geeks",                                  "for", "geeks" };    printDuplicates(words);    return 0;}
Output:  
geeks
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STL
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