Count Items Matching a Rule

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ArraysStrings

You are given an array items, where each items[i] = [type_i, color_i, name_i] describes the type, color, and name of the i^th item. You are also given a rule represented by two strings, ruleKey and ruleValue.

The i^th item is said to match the rule if one of the following is true:

ruleKey == "type" and ruleValue == type_i.
ruleKey == "color" and ruleValue == color_i.
ruleKey == "name" and ruleValue == name_i.

Return the number of items that match the given rule.

Example 1:

Input: items = [["phone","blue","pixel"],["computer","silver","lenovo"],["phone","gold","iphone"]], ruleKey = "color", ruleValue = "silver"
Output: 1
Explanation: There is only one item matching the given rule, which is ["computer","silver","lenovo"].

Example 2:

Input: items = [["phone","blue","pixel"],["computer","silver","phone"],["phone","gold","iphone"]], ruleKey = "type", ruleValue = "phone"
Output: 2
Explanation: There are only two items matching the given rule, which are ["phone","blue","pixel"] and ["phone","gold","iphone"]. Note that the item ["computer","silver","phone"] does not match.

Constraints:

1 <= items.length <= 10⁴
1 <= type_i.length, color_i.length, name_i.length, ruleValue.length <= 10
ruleKey is equal to either "type", "color", or "name".
All strings consist only of lowercase letters.

Try coding it in LeetCode

Solution

Clarifying Questions

When you get asked this question in a real-life environment, it will often be ambiguous (especially at FAANG). Make sure to ask these questions in that case:

What are the possible values and data types for the ruleKey and ruleValue?
Are the values in each item's list guaranteed to be of the same data type as the ruleValue?
Can the input array items be empty or null?
What is the expected behavior if the input array is null or empty?
Are the strings in the 'items' array and ruleValue case-sensitive?

Brute Force Solution

Approach

The brute force method for this problem involves checking every single item to see if it matches the rule. It's like manually looking at each item and comparing its properties to what the rule requires. We count each time an item fits the description.

Here's how the algorithm would work step-by-step:

Take the first item in the list.
Check if the property specified in the rule matches the corresponding value in the item.
If the property and value match, increase the count by one.
Repeat steps 1-3 for every item in the list.
After checking all items, the count represents the number of items that matched the rule.

Code Implementation

def count_items_matching_rule_brute_force(items, rule_key_index, rule_value): 
    number_of_matching_items = 0

    for item in items:
        # Access the correct property based on the rule key index
        item_property = item[rule_key_index]

        # Check if the property matches the given value
        if item_property == rule_value:

            #Increment the counter when properties match
            number_of_matching_items += 1

    return number_of_matching_items

Big(O) Analysis

Time Complexity

O(n) – The provided solution iterates through each item in the input list once. For each of the n items in the list, it performs a constant amount of work: comparing a property of the item to the specified rule value. Therefore, the time complexity is directly proportional to the number of items in the list, n, resulting in a linear time complexity of O(n).

Space Complexity

O(1) – The algorithm iterates through the list of items, checking each one against the rule. It maintains a single integer variable to store the count of matching items. This count variable occupies a constant amount of space, irrespective of the number of items in the input list. Therefore, the auxiliary space complexity is O(1).

Optimal Solution

Approach

To solve this problem efficiently, we need to check each item and see if it matches the rule. Instead of checking every single detail for each item, we'll focus on the specific detail the rule cares about and compare it directly.

Here's how the algorithm would work step-by-step:

First, figure out what part of the item description the rule is looking at (like the type, color, or name).
Go through each item in the list one by one.
For each item, look only at the part of the description that the rule is interested in.
Compare that specific detail to the value given in the rule.
If the detail matches the rule's value, then increase our count of matching items by one.
Once you have checked all the items, the final count will tell you how many items matched the rule.

Code Implementation

def count_matches(items, rule_key, rule_value): 
    match_count = 0

    for item in items:
        # Determine the index based on the rule key.
        if rule_key == "type":
            index_to_check = 0

        elif rule_key == "color":
            index_to_check = 1

        else:
            index_to_check = 2

        # Compare the item's value to the rule value.
        if item[index_to_check] == rule_value:
            # Increment the counter because we found a match
            match_count += 1

    return match_count

Big(O) Analysis

Time Complexity

O(n) – The dominant operation is iterating through each of the n items in the list. For each item, we perform a constant-time comparison to check if it matches the specified rule. Since the number of items to check directly scales with the input size n and each comparison is constant time, the overall time complexity is O(n).

Space Complexity

O(1) – The algorithm iterates through the input list of items, examining each item's properties. It only uses a constant amount of extra space to store the count of matching items. No auxiliary data structures like lists, maps, or recursion are utilized, and the space required doesn't depend on the number of items (N). Therefore, the space complexity is O(1), indicating constant extra space usage.

Edge Cases

Case	How to Handle
Null or empty items list	Return 0 immediately as no items can match any rule.
Null or empty ruleKey or ruleValue	If either is null or empty, consider it an invalid input and return 0, or throw an exception depending on requirements.
items list containing null or empty inner lists	Handle null or empty inner lists by skipping them or returning an error, depending on desired behavior.
Rule key is not one of the expected strings (type, color, name)	Return 0 or throw an exception indicating an invalid ruleKey.
Large items list (performance considerations)	Ensure the chosen algorithm has a time complexity that scales reasonably with the size of the items list (e.g., O(n)).
Items list with very long strings (memory considerations)	Be mindful of memory usage if the strings are extremely long, potentially impacting performance or causing memory errors.
Case sensitivity of ruleValue (if applicable)	Convert both the item value and ruleValue to lowercase for case-insensitive comparison, if required.
Items list with mixed data types in the inner lists (e.g., numbers instead of strings)	Handle type checking of the values within the inner lists to ensure they are strings, and convert if necessary or return an error if conversion is not possible.

Null or empty items list

How to Handle:

Return 0 immediately as no items can match any rule.

Null or empty ruleKey or ruleValue

How to Handle:

If either is null or empty, consider it an invalid input and return 0, or throw an exception depending on requirements.

items list containing null or empty inner lists

How to Handle:

Handle null or empty inner lists by skipping them or returning an error, depending on desired behavior.

Rule key is not one of the expected strings (type, color, name)

How to Handle:

Return 0 or throw an exception indicating an invalid ruleKey.

Large items list (performance considerations)

How to Handle:

Ensure the chosen algorithm has a time complexity that scales reasonably with the size of the items list (e.g., O(n)).

Items list with very long strings (memory considerations)

How to Handle:

Be mindful of memory usage if the strings are extremely long, potentially impacting performance or causing memory errors.

Case sensitivity of ruleValue (if applicable)

How to Handle:

Convert both the item value and ruleValue to lowercase for case-insensitive comparison, if required.

Items list with mixed data types in the inner lists (e.g., numbers instead of strings)

How to Handle:

Handle type checking of the values within the inner lists to ensure they are strings, and convert if necessary or return an error if conversion is not possible.