Count Common Words With One Occurrence.cpp

class Solution {
public:
    int countWords(vector<string>& words1, vector<string>& words2) {
        unordered_map<string, int> freq1, freq2; 
        for (auto& s : words1) ++freq1[s]; 
        for (auto& s : words2) ++freq2[s]; 
        int ans = 0; 
        for (auto& [s, v] : freq1) 
            if (v == 1 && freq2[s] == 1) ++ans; 
        return ans; 
    }
};