Question

2408. Design SQL

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Description

You are given n tables represented with two arrays names and columns, where names[i] is the name of the ith table and columns[i] is the number of columns of the ith table.

You should be able to perform the following operations:

• Insert a row in a specific table. Each row you insert has an id. The id is assigned using an auto-increment method where the id of the first inserted row is 1, and the id of each other row inserted into the same table is the id of the last inserted row (even if it was deleted) plus one.
• Delete a row from a specific table. Note that deleting a row does not affect the id of the next inserted row.
• Select a specific cell from any table and return its value.

Implement the SQL class:

• SQL(String[] names, int[] columns) Creates the n tables.
• void insertRow(String name, String[] row) Adds a row to the table name. It is guaranteed that the table will exist, and the size of the array row is equal to the number of columns in the table.
• void deleteRow(String name, int rowId) Removes the row rowId from the table name. It is guaranteed that the table and row will exist.
• String selectCell(String name, int rowId, int columnId) Returns the value of the cell in the row rowId and the column columnId from the table name.

 

Example 1:

Input
["SQL", "insertRow", "selectCell", "insertRow", "deleteRow", "selectCell"]
[[["one", "two", "three"], [2, 3, 1]], ["two", ["first", "second", "third"]], ["two", 1, 3], ["two", ["fourth", "fifth", "sixth"]], ["two", 1], ["two", 2, 2]]
Output
[null, null, "third", null, null, "fifth"]

Explanation
SQL sql = new SQL(["one", "two", "three"], [2, 3, 1]); // creates three tables.
sql.insertRow("two", ["first", "second", "third"]); // adds a row to the table "two". Its id is 1.
sql.selectCell("two", 1, 3); // return "third", finds the value of the third column in the row with id 1 of the table "two".
sql.insertRow("two", ["fourth", "fifth", "sixth"]); // adds another row to the table "two". Its id is 2.
sql.deleteRow("two", 1); // deletes the first row of the table "two". Note that the second row will still have the id 2.
sql.selectCell("two", 2, 2); // return "fifth", finds the value of the second column in the row with id 2 of the table "two".

 

Constraints:

• n == names.length == columns.length
• 1 <= n <= 104
• 1 <= names[i].length, row[i].length, name.length <= 20
• names[i], row[i], and name consist of lowercase English letters.
• 1 <= columns[i] <= 100
• All the strings of names are distinct.
• name exists in the array names.
• row.length equals the number of columns in the chosen table.
• rowId and columnId will be valid.
• At most 250 calls will be made to insertRow and deleteRow.
• At most 104 calls will be made to selectCell.

Solutions

Solution 1: Hash Table

Create a hash table tables to store the mapping of table names to table data rows. Directly simulate the operations in the problem.

The time complexity of each operation is $O(1)$, and the space complexity is $O(n)$.

class SQL:
  def __init__(self, names: List[str], columns: List[int]):
    self.tables = defaultdict(list)

  def insertRow(self, name: str, row: List[str]) -> None:
    self.tables[name].append(row)

  def deleteRow(self, name: str, rowId: int) -> None:
    pass

  def selectCell(self, name: str, rowId: int, columnId: int) -> str:
    return self.tables[name][rowId - 1][columnId - 1]


# Your SQL object will be instantiated and called as such:
# obj = SQL(names, columns)
# obj.insertRow(name,row)
# obj.deleteRow(name,rowId)
# param_3 = obj.selectCell(name,rowId,columnId)

class SQL {
  private Map<String, List<List<String>>> tables;

  public SQL(List<String> names, List<Integer> columns) {
    tables = new HashMap<>(names.size());
  }

  public void insertRow(String name, List<String> row) {
    tables.computeIfAbsent(name, k -> new ArrayList<>()).add(row);
  }

  public void deleteRow(String name, int rowId) {
  }

  public String selectCell(String name, int rowId, int columnId) {
    return tables.get(name).get(rowId - 1).get(columnId - 1);
  }
}

/**
 * Your SQL object will be instantiated and called as such:
 * SQL obj = new SQL(names, columns);
 * obj.insertRow(name,row);
 * obj.deleteRow(name,rowId);
 * String param_3 = obj.selectCell(name,rowId,columnId);
 */

class SQL {
public:
  unordered_map<string, vector<vector<string>>> tables;
  SQL(vector<string>& names, vector<int>& columns) {
  }

  void insertRow(string name, vector<string> row) {
    tables[name].push_back(row);
  }

  void deleteRow(string name, int rowId) {
  }

  string selectCell(string name, int rowId, int columnId) {
    return tables[name][rowId - 1][columnId - 1];
  }
};

/**
 * Your SQL object will be instantiated and called as such:
 * SQL* obj = new SQL(names, columns);
 * obj->insertRow(name,row);
 * obj->deleteRow(name,rowId);
 * string param_3 = obj->selectCell(name,rowId,columnId);
 */

type SQL struct {
  tables map[string][][]string
}

func Constructor(names []string, columns []int) SQL {
  return SQL{map[string][][]string{}}
}

func (this *SQL) InsertRow(name string, row []string) {
  this.tables[name] = append(this.tables[name], row)
}

func (this *SQL) DeleteRow(name string, rowId int) {

}

func (this *SQL) SelectCell(name string, rowId int, columnId int) string {
  return this.tables[name][rowId-1][columnId-1]
}

/**
 * Your SQL object will be instantiated and called as such:
 * obj := Constructor(names, columns);
 * obj.InsertRow(name,row);
 * obj.DeleteRow(name,rowId);
 * param_3 := obj.SelectCell(name,rowId,columnId);
 */