add chapter9 exercises

chapter9/examples/heaptest.py

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+import heapq
+
+customers = []
+heapq.heappush(customers, (2, "Harry"))
+heapq.heappush(customers, (3, "Charles"))
+heapq.heappush(customers, (1, "Riya"))
+heapq.heappush(customers, (4, "Stacy"))
+
+while customers:
+    print(heapq.heappop(customers))

chapter9/examples/list.py

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+customers = []
+customers.append((2, "Harry"))  # no sort needed here because 1 item.
+customers.append((3, "Charles"))
+customers.sort(reverse=True)
+# Need to sort to maintain order
+customers.append((1, "Riya"))
+customers.sort(reverse=True)
+# Need to sort to maintain order
+customers.append((4, "Stacy"))
+customers.sort(reverse=True)
+
+while customers:
+    print(customers.pop(0))
+# Will print names in the order: Stacy, Charles, Harry, Riya.

chapter9/examples/priorityqueuetest.py

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+from queue import PriorityQueue
+
+customers = (
+    PriorityQueue()
+)  # we initialise the PQ class instead of using a function to operate upon a list.
+customers.put((2, "Harry"))
+customers.put((3, "Charles"))
+customers.put((1, "Riya"))
+customers.put((4, "Stacy"))
+
+while customers:
+    print(customers.get())