18 and 20

18.py

+# Write a function solve that generates the first n rows of Pascal's Triangle.
+
+def solve(rows):
+    triangle = []
+    for i in range(0, rows):
+        row = []
+        row.append(1)
+        if i == 1:
+            row.append(1)
+        elif i > 1:
+            for j in range(0, i-1):
+                first = triangle[i-1][j]
+                second = triangle[i-1][j+1]
+                row.append(first + second)
+            row.append(1)
+        triangle.append(row)
+    return triangle

20.py

+# Write a function that, given the head of a singly linked list, reverses the list. 
+# Return the root node of the reversed list.
+
+def solve(head):
+    current = head
+    prev = None
+
+    while current:
+        temp_next = current.next
+        current.next = prev
+
+        prev = current
+        current = temp_next
+    return prev
+