Count words that appear exactly two times in an array of words

Given an array of n words. Some words are repeated twice, we need count such words.

Input : s[] = {"hate", "love", "peace", "love", 
               "peace", "hate", "love", "peace", 
               "love", "peace"};
Output : 1
There is only one word "hate" that appears twice

Input : s[] = {"Om", "Om", "Shankar", "Tripathi", 
                "Tom", "Jerry", "Jerry"};
Output : 2
There are two words "Om" and "Jerry" that appear

Source : Amazon Interview

  1. Traverse the given array, store counts of words in a hash table
  2. Traverse hash table and count all words with count 2.

Below is C++ implementation.

// C++ program to count all words with count
// exavtly 2.
#include <bits/stdc++.h>
using namespace std;

// Returns count of words with frequency
// exactly 2.
int countWords(string str[], int n)
    unordered_map<string, int> m;
    for (int i = 0; i < n; i++)
        m[str[i]] += 1;

    int res = 0;
    for (auto it = m.begin(); it != m.end(); it++)
        if ((it->second == 2))

    return res;

// Driver code
int main()
    string s[] = { "hate", "love", "peace", "love",
                   "peace", "hate", "love", "peace",
                   "love", "peace" };
    int n = sizeof(s) / sizeof(s[0]);
    cout << countWords(s, n);
    return 0;



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