Feat/28 days later python solution -> main

README.md

@@ -33,7 +33,7 @@ Feel free to explore, learn, and share your own approaches.
 - [x] **3/25:** Opening Day ⚾️
 - [ ] **3/26:** Flatten Array 🪜
 - [ ] **3/27:** Infinite Monkey Theorem 🐒
-- [ ] **3/28:** 28 Days Later 🧟
+- [x] **3/28:** [28 Days Later](https://github.com/codedex-io/daily-challenges/tree/main/march-2026/3-28-28-days-later) 🧟
 - [ ] **3/29:** ❓❓❓
 - [ ] **3/30:** ❓❓❓
 - [ ] **3/31:** ❓❓❓

march-2026/3-28-28-days-later/28-days-later.py

@@ -0,0 +1,37 @@
+def days_to_infect(city):
+  days = 0
+
+  while True:
+    # list to store who gets infected this round
+    newly_infected = []
+
+    # for each cell in the grid
+    for i in range(len(city)):
+      for j in range(len(city[i])):
+        if city[i][j] == '🧟':
+          # check the 4 neighbors
+          if i > 0 and city[i-1][j] == '👤':
+            newly_infected.append((i-1, j))
+          if i < len(city) - 1 and city[i+1][j] == '👤':
+            newly_infected.append((i+1, j))
+          if j > 0 and city[i][j-1] == '👤':
+            newly_infected.append((i, j-1))
+          if j < len(city[i]) - 1 and city[i][j+1] == '👤':
+            newly_infected.append((i, j+1))
+
+    # if nobody new go infected, spreading has stopped
+    if not newly_infected:
+      break
+
+    # infect everyone in the list at the same time
+    for i, j in newly_infected:
+      city[i][j] = '🧟'
+
+    days += 1
+
+  # if any healthy people are left, they can never be reached
+  for i in city:
+    if '👤' in i:
+      return -1
+
+  return days