# LeetCode 1773. Count Items Matching a Rule

## Description

https://leetcode.com/problems/count-items-matching-a-rule/

You are given an array `items`, where each `items[i] = [typei, colori, namei]` describes the type, color, and name of the `ith` item. You are also given a rule represented by two strings, `ruleKey` and `ruleValue`.

The `ith` item is said to match the rule if one of the following is true:

• `ruleKey == "type"` and `ruleValue == typei`.
• `ruleKey == "color"` and `ruleValue == colori`.
• `ruleKey == "name"` and `ruleValue == namei`.

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 <= typei.length, colori.length, namei.length, ruleValue.length <= 10`
• `ruleKey` is equal to either `"type"``"color"`, or `"name"`.
• All strings consist only of lowercase letters.

## Explanation

Just count how many elements have the demanding rule key and value.

## Python Solution

``````class Solution:
def countMatches(self, items: List[List[str]], ruleKey: str, ruleValue: str) -> int:

rule_mapping = {
"type": 0,
"color": 1,
"name": 2
}

count = 0
for item in items:
if item[rule_mapping[ruleKey]] == ruleValue:
count += 1

return count``````
• Time Complexity: O(N).
• Space Complexity: O(1).