completed assignment

force-app/main/default/triggers/ValidateAccount.trigger

@@ -0,0 +1,31 @@
+trigger ValidateAccount on Account (before insert) {
+    Set<String> accountNames = new Set<String>();
+
+    for (Account account : Trigger.New)
+    {
+        if (accountNames.contains(account.Name))
+        {
+            account.Name.addError('Account name already exists!');
+        } 
+        else {
+            accountNames.add(account.Name);
+        }
+    }
+
+    List<Account> existingAccounts = [
+        SELECT Id, Name 
+        FROM Account 
+        WHERE Name IN :accountNames
+    ];
+
+    for (Account account : Trigger.New) 
+    {
+        for (Account existingAccount : existingAccounts)
+        {
+            if (account.Name == existingAccount.Name && account.Id != existingAccount.Id)
+            {
+                account.Name.addError('Account name already exists!');
+            }
+        }
+    }
+}