Check Array Formation Through Concatenation LeetCode solution in Python

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class Solution:
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    def canFormArray(self, arr: List[int], pieces: List[List[int]]) -> bool:
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        keys, ans = {}, []
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        for piece in pieces:
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            keys[piece[0]] = piece
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        for a in arr:
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            if a in keys:
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                ans.extend(keys[a])
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        return "".join(map(str, arr)) == "".join(map(str, ans))