2085. Count Common Words With One Occurrence 

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class Solution {
    public int countWords(String[] words1, String[] words2) {
        Map<String, Integer> countMap1 = new HashMap<>(), countMap2 = new HashMap<>();

        for (String word : words1) {
            countMap1.put(word, countMap1.getOrDefault(word, 0) + 1);
        }
        for (String word : words2) {
            countMap2.put(word, countMap2.getOrDefault(word, 0) + 1);
        }

        int count = 0;
        for (Map.Entry<String, Integer> entry : countMap1.entrySet()) {
            if (entry.getValue() == 1 && countMap2.getOrDefault(entry.getKey(), 0) == 1) {
                count++;
            }
        }

        return count;
    }
}

References

2085. Count Common Words With One Occurrence