Count Common Words With One Occurrence

You are given two arrays of strings, words1 and words2.

A string w is considered a match if it appears in words1 exactly once and also appears in words2 exactly once. Return the number of distinct strings that satisfy this match condition.

Notes:

• A word that shows up twice or more in either array can never count as a match, even if it also shows up once in the other array.
• Comparisons are exact string comparisons (case-sensitive), and each qualifying word is counted only once regardless of how many times it would otherwise repeat.

Examples

Example 1:

Input: words1 = ["kite","echo","echo","lamp"], words2 = ["lamp","kite","drum"]

Output: 2

Explanation:

• "kite" appears once in words1 and once in words2 — counts.
• "echo" appears twice in words1, so it is disqualified even though it's absent from words2.
• "lamp" appears once in words1 and once in words2 — counts.
• "drum" only appears in words2, so it doesn't matter how many times — no match in words1.

Total matches: "kite" and "lamp", so the answer is 2.

Example 2:

Input: words1 = ["cat","cat","dog"], words2 = ["dog","dog","cat"]

Output: 0

Explanation:

• "cat" appears twice in words1, so it fails the exactly-once rule for words1.
• "dog" appears once in words1 but twice in words2, so it fails the exactly-once rule for words2.

No word satisfies both conditions, so the answer is 0.

Constraints

• 1 <= words1.length, words2.length <= 1000
• 1 <= words1[i].length, words2[j].length <= 30
• Each word consists of lowercase English letters only.