Auto-solve daily LeetCode problem using GPT-5-mini

Author: jeremymanning

problems/3606/gpt5-mini.md

@@ -0,0 +1,59 @@
+# [Problem 3606: Coupon Code Validator](https://leetcode.com/problems/coupon-code-validator/description/?envType=daily-question)
+
+## Initial thoughts (stream-of-consciousness)
+We need to filter coupons by three conditions: code validity (non-empty and only alphanumeric/underscore), business line membership in one of four allowed categories, and isActive true. After filtering we must order results first by business line in a specified non-alphabetical order, then lexicographically by the code string within each business line. A straightforward approach is to iterate over the arrays, validate each coupon, collect the valid ones along with an ordering key for business line, then sort by (businessLineOrder, code). Regex or manual character checks can validate the code characters.
+
+## Refining the problem, round 2 thoughts
+- Business line matching is case-sensitive as problem examples use lowercase; assume we require exact match to the four allowed strings.
+- Code validation: use regex ^[A-Za-z0-9_]+$ to ensure non-empty and only allowed characters. Beware empty string should be rejected.
+- Sorting: create an order mapping {'electronics':0, 'grocery':1, 'pharmacy':2, 'restaurant':3} and sort by tuple (order, code).
+- Complexity: n up to 100 so even simple approaches are fine. Sorting dominates: O(n log n) comparisons, each comparison may inspect strings up to length 100.
+- Edge cases: empty code, invalid characters, invalid businessLine, inactive coupons — all filtered out. If none valid, return empty list.
+
+## Attempted solution(s)
+```python
+import re
+from typing import List
+
+class Solution:
+    def validateCoupon(self, code: List[str], businessLine: List[str], isActive: List[bool]) -> List[str]:
+        """
+        Returns list of valid coupon codes sorted by business line order and then lexicographically by code.
+        """
+        # Define required business line order
+        order = {
+            "electronics": 0,
+            "grocery": 1,
+            "pharmacy": 2,
+            "restaurant": 3
+        }
+        # Regex to validate code: non-empty, only letters, digits, and underscore
+        pattern = re.compile(r'^[A-Za-z0-9_]+$')
+        
+        n = len(code)
+        valid = []
+        
+        for i in range(n):
+            if not isActive[i]:
+                continue
+            bl = businessLine[i]
+            if bl not in order:
+                continue
+            c = code[i]
+            if not c:
+                continue
+            if not pattern.match(c):
+                continue
+            # store (businessLineOrder, code) for sorting
+            valid.append((order[bl], c))
+        
+        # sort by business line order, then lexicographically by code
+        valid.sort(key=lambda x: (x[0], x[1]))
+        # return only codes in sorted order
+        return [c for _, c in valid]
+```
+- Notes:
+  - Approach: iterate, validate each coupon with simple checks and a regex for code characters, collect valid entries along with a numeric business-line order, sort by that tuple, then extract codes.
+  - Time complexity: O(n log n) due to sorting, where n is number of coupons. Each validation uses O(L) where L ≤ 100 (length of code), so overall dominated by sort comparisons.
+  - Space complexity: O(n) extra space to hold valid coupons before sorting.
+  - Implementation details: businessLine match is exact (case-sensitive). Regex ensures non-empty and only allowed characters (alphanumeric and underscore).