13.py

+# Write a function solve that returns the running sum of a list. 
+# The running sum is the sum of all elements up to each index.
+
+def solve(nums):
+    result = [nums[0]]
+    for i in range(1, len(nums)):
+        result.append(result[i - 1] + nums[i])
+    return result
\ No newline at end of file

14.py

+# Write a function solve that reverses the words in a string. 
+# Words are separated by spaces.
+
+def solve(string):
+    list = reversed(string.split())
+    return ' '.join(list)
\ No newline at end of file

15.py

+# Write a function solve that rotates an n x n matrix 90 degrees clockwise in-place.
+
+def solve(matrix):
+    for i in range(int(len(matrix))):
+        for j in range(i):
+            matrix[i][j], matrix[j][i] = matrix[j][i], matrix[i][j]
+    for list in matrix:
+        list.reverse()
+    return matrix
+

17.py

+# Write a function solve that counts the number of vowels (a,e,i,o,u) in a string, ignoring case.
+
+def solve(string):
+    counter = 0
+    vowels = ["a","e","i","o","u"]
+    for char in string.lower():
+        if char in vowels:
+            counter += 1
+    return counter

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
+