884. Uncommon Words from Two Sentences - Explanation

1. Hash Map - I

class Solution:
    def uncommonFromSentences(self, s1: str, s2: str) -> List[str]:
        count = defaultdict(int)
        for w in s1.split(" ") + s2.split(" "):
            count[w] += 1

        res = []
        for w, cnt in count.items():
            if cnt == 1:
                res.append(w)
        return res

Time & Space Complexity

Time complexity: $O(n + m)$
Space complexity: $O(n + m)$

Where $n$ and $m$ are the lengths of the strings $s1$ and $s2$ , respectively.

2. Hash Map - II

class Solution:
    def uncommonFromSentences(self, s1: str, s2: str) -> List[str]:
        return [w for w, cnt in Counter(s1.split(" ") + s2.split(" ")).items() if cnt == 1]

Time & Space Complexity

Time complexity: $O(n + m)$
Space complexity: $O(n + m)$

Where $n$ and $m$ are the lengths of the strings $s1$ and $s2$ , respectively.