code from chapter 4

04_quicksort/python/01_loop_sum.py

@@ -0,0 +1,7 @@
+def sum(arr):
+  total = 0
+  for x in arr:
+    total += x
+  return total
+
+print sum([1, 2, 3, 4])

04_quicksort/python/02_recursive_sum.py

@@ -0,0 +1,4 @@
+def sum(list):
+  if list == []:
+    return 0
+  return list[0] + sum(list[1:])

04_quicksort/python/03_recursive_count.py

@@ -0,0 +1,4 @@
+def count(list):
+  if list == []:
+    return 0
+  return 1 + count(list[1:])

04_quicksort/python/04_recursive_max.py

@@ -0,0 +1,5 @@
+def max(list):
+  if len(list) == 2:
+    return list[0] if list[0] > list[1] else list[1]
+  sub_max = max(list[1:])
+  return list[0] if list[0] > sub_max else sub_max

04_quicksort/python/05_quicksort.py

@@ -0,0 +1,14 @@
+def quicksort(array):
+  if len(array) < 2:
+    # base case, arrays with 0 or 1 element are already "sorted"
+    return array
+  else:
+    # recursive case
+    pivot = array[0]
+    # sub-array of all the elements less than the pivot
+    less = [i for i in array[1:] if i <= pivot]
+    # sub-array of all the elements greater than the pivot
+    greater = [i for i in array[1:] if i > pivot]
+    return quicksort(less) + [pivot] + quicksort(greater)
+
+print quicksort([10, 5, 2, 3])