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import sqlite3

def get_user(username):
    conn = sqlite3.connect("users.db")
    cursor = conn.cursor()
    query = f"SELECT * FROM users WHERE username = '{username}'"
    cursor.execute(query)
    user = cursor.fetchone()
    return user

import sqlite3
from typing import Optional

def get_user(username: str) -> Optional[tuple]:
    """
    Retrieve user from database securely using parameterized query.
    
    Args:
        username: Username to search (validated input)
    
    Returns:
        User tuple or None if not found
    """
    # Input validation
    if not username or not username.isalnum():
        raise ValueError("Invalid username format")
    
    try:
        with sqlite3.connect("users.db") as conn:
            cursor = conn.cursor()
            # Use parameterized query to prevent SQL injection
            query = "SELECT * FROM users WHERE username = ?"
            cursor.execute(query, (username,))
            return cursor.fetchone()
    except sqlite3.Error as e:
        logging.error(f"Database error: {e}")
        raise

function processUsers(users) {
  let results = [];
  for (let i = 0; i < users.length; i++) {
    for (let j = 0; j < users.length; j++) {
      if (users[i].id === users[j].managerId) {
        results.push({
          employee: users[i].name,
          manager: users[j].name
        });
      }
    }
  }
  return results;
}

/**
 * Maps employees to their managers efficiently.
 * @param {Array<{id: number, name: string, managerId: number}>} users
 * @returns {Array<{employee: string, manager: string}>}
 */
function processUsers(users) {
  // Create O(1) lookup map: managerId -> manager object
  const managerMap = new Map(
    users.map(user => [user.id, user])
  );
  
  // Single pass through users array
  return users
    .filter(user => user.managerId && managerMap.has(user.managerId))
    .map(user => ({
      employee: user.name,
      manager: managerMap.get(user.managerId).name
    }));
}