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int n = arr.size();
        unordered_map<int, vector<int>> mapping;
        // initialize hashmap
        for (auto p: pieces){
            mapping[p[0]] = p;
        }

        int i = 0;
        while (i < n) {
            // find target piece
            if (mapping.count(arr[i])==0) {
                return false;
            }
            // check target piece
            auto targetPiece = mapping[arr[i]];
            for (int x : targetPiece) {
                if (x != arr[i]) {
                    return false;
                }
                i++;
            }
        }
        return true;