Negative keywords for cost control in Digital Marketing - Time & Space Complexity

Time Complexity: Negative keywords for cost control

O(n)

Understanding Time Complexity

When using negative keywords in digital marketing, it's important to understand how the process scales as you add more keywords.

We want to know how the time to check and filter ads grows when the list of negative keywords grows.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

for each search_query in user_searches:
    for each negative_keyword in negative_keywords_list:
        if negative_keyword in search_query:
            exclude ad from showing
            break
    else:
        show ad
    

This code checks every user search against all negative keywords to decide if an ad should be shown or blocked.

Identify Repeating Operations

• Primary operation: Checking each search query against all negative keywords.
• How many times: For every search query, the code loops through the entire negative keywords list until a match is found or the list ends.

How Execution Grows With Input

As the number of negative keywords grows, the time to check each search query grows roughly in proportion.

Input Size (number of negative keywords)	Approx. Operations per search query
10	About 10 checks
100	About 100 checks
1000	About 1000 checks

Pattern observation: The number of checks grows linearly as the negative keywords list grows.

Final Time Complexity

Time Complexity: O(n)

This means the time to filter ads grows directly in proportion to the number of negative keywords.

Common Mistake

[X] Wrong: "Adding more negative keywords won't affect how fast ads are filtered because computers are fast."

[OK] Correct: Even though computers are fast, checking more keywords takes more time, so performance slows down as the list grows.

Interview Connect

Understanding how filtering scales with negative keywords helps you design efficient ad campaigns and shows you can think about performance in real marketing systems.

Self-Check

"What if we used a special data structure like a hash set for negative keywords? How would the time complexity change?"

Practice

1. What is the main purpose of using negative keywords in digital marketing campaigns?

easy

A. To increase the number of ads shown

B. To prevent ads from showing on irrelevant searches

C. To raise the bid price automatically

D. To target new customer segments

Solution

1. Step 1: Understand the role of negative keywords

   Negative keywords are used to exclude certain search terms that are not relevant to the ad campaign.

2. Step 2: Identify the effect on ad display

   By excluding irrelevant searches, ads do not show to uninterested users, saving budget and improving targeting.

3. Final Answer:

   To prevent ads from showing on irrelevant searches -> Option B

4. Quick Check:

   Negative keywords block irrelevant searches = A [OK]

Hint: Negative keywords stop ads on unwanted searches [OK]

Common Mistakes:

• Thinking negative keywords increase ad impressions
• Confusing negative keywords with bid adjustments
• Believing negative keywords target new customers

2. Which of the following is the correct way to add a negative keyword in a Google Ads campaign?

easy

A. Add the keyword under the 'Positive Keywords' section

B. Include the keyword in the ad headline

C. Add the keyword under the 'Negative Keywords' list

D. Increase the bid for the keyword

Solution

1. Step 1: Locate where negative keywords are managed

   Negative keywords must be added specifically in the 'Negative Keywords' list or section in the campaign settings.

2. Step 2: Confirm the correct placement

   Adding keywords under 'Positive Keywords' or in ad text does not exclude them; only the negative list blocks them.

3. Final Answer:

   Add the keyword under the 'Negative Keywords' list -> Option C

4. Quick Check:

   Negative keywords go in negative list = B [OK]

Hint: Negative keywords must be in the negative list section [OK]

Common Mistakes:

• Adding negative keywords as positive keywords
• Trying to exclude keywords by changing ad text
• Increasing bids instead of excluding keywords

3. A campaign has the negative keyword free added. Which search query will NOT trigger the ad?

medium

A. free shoes giveaway

B. buy shoes online

C. discount shoes sale

D. shoes for running

Solution

1. Step 1: Understand the effect of the negative keyword 'free'

   The negative keyword 'free' blocks any search queries containing the word 'free'.

2. Step 2: Check each option for the word 'free'

   free shoes giveaway contains 'free', so the ad will not show for that query. Other options do not contain 'free'.

3. Final Answer:

   free shoes giveaway -> Option A

4. Quick Check:

   Query with 'free' blocked = A [OK]

Hint: Searches containing negative keywords won't show ads [OK]

Common Mistakes:

• Ignoring the presence of the negative keyword in queries
• Assuming all queries trigger ads regardless of negatives
• Confusing negative keywords with positive targeting

4. A marketer added the negative keyword cheap but still sees ads showing for "cheap shoes" searches. What is the likely error?

medium

A. Negative keyword was added as a broad match instead of exact match

B. Negative keyword was added to the wrong campaign or ad group

C. Negative keyword was misspelled or has extra spaces

D. All of the above

Solution

1. Step 1: Check common reasons negative keywords fail

   Negative keywords may not work if added to the wrong place, misspelled, or match type is incorrect.

2. Step 2: Understand that all listed errors can cause ads to show

   Any of these mistakes can cause ads to still appear for excluded terms.

3. Final Answer:

   All of the above -> Option D

4. Quick Check:

   Multiple errors cause negative keyword failure = D [OK]

Hint: Check placement, spelling, and match type for negatives [OK]

Common Mistakes:

• Assuming one error type only
• Not verifying campaign or ad group assignment
• Ignoring match type differences

5. A company wants to reduce wasted ad spend on irrelevant searches for "luxury watches" but still attract serious buyers. Which negative keyword strategy is best?

hard

A. Add broad negative keywords like 'cheap', 'free', and 'replica' to exclude low-value searches

B. Add all possible negative keywords including brand names of competitors

C. Remove all negative keywords to maximize ad reach

D. Add only exact match negative keywords for 'luxury watches'

Solution

1. Step 1: Identify goal to reduce irrelevant clicks but keep serious buyers

   Excluding terms like 'cheap', 'free', and 'replica' blocks users unlikely to buy luxury watches.

2. Step 2: Evaluate options for effectiveness and risks

   Add broad negative keywords like 'cheap', 'free', and 'replica' to exclude low-value searches targets low-value searches broadly without blocking serious buyers. Add all possible negative keywords including brand names of competitors risks blocking competitor interest but may exclude potential customers. Remove all negative keywords to maximize ad reach wastes budget. Add only exact match negative keywords for 'luxury watches' is too narrow to exclude irrelevant searches.

3. Final Answer:

   Add broad negative keywords like 'cheap', 'free', and 'replica' to exclude low-value searches -> Option A

4. Quick Check:

   Broad negatives exclude irrelevant, keep buyers = C [OK]

Hint: Use broad negatives to block low-value searches [OK]

Common Mistakes:

• Adding too many negatives blocking good traffic
• Removing negatives and wasting budget
• Using only exact match negatives missing many irrelevant queries