adds chapter9 exercises with heap and without

chapter9/with_heap/ex171a.py

@@ -0,0 +1,51 @@
+import heapq
+import logging
+import math
+
+logging.basicConfig(level=logging.DEBUG)
+logger = logging.getLogger(__name__)
+
+graph = {
+    "start": {"a": 5, "b": 2},
+    "a": {"b": 8, "c": 4, "d": 2},
+    "b": {"a": 8, "d": 7},
+    "c": {"d": 6, "fin": 3},
+    "d": {"fin": 1},
+    "fin": {},
+}
+
+
+def dijkstra(graph, node):
+    costs = {node: math.inf for node in graph}
+    costs[node] = 0
+    parents = {node: None for node in graph}
+    queue = [(0, node)]
+
+    while queue:
+        current_cost, current_node = heapq.heappop(queue)
+
+        for next_node, weight in graph[current_node].items():
+            new_cost = current_cost + weight
+            if new_cost < costs[next_node]:
+                costs[next_node] = new_cost
+                parents[next_node] = current_node
+                heapq.heappush(queue, (new_cost, next_node))
+    return costs, parents
+
+
+costs, parents = dijkstra(graph, "start")
+
+print(f"lowest cost route: {costs['fin']}")
+
+
+def get_full_route():
+    route = []
+    next = "fin"
+    while next != "start":
+        route.append(next)
+        next = parents[next]
+    route.append("start")
+    return list(reversed(route))
+
+
+print(f"route: {get_full_route()}")

chapter9/with_heap/ex171b.py

@@ -0,0 +1,36 @@
+import heapq
+import logging
+import math
+
+logging.basicConfig(level=logging.DEBUG)
+logger = logging.getLogger(__name__)
+
+graph = {
+    "start": {"a": 10},
+    "a": {"c": 20},
+    "b": {"a": 1, "c": 1},
+    "c": {"b": 1, "fin": 30},
+    "fin": {},
+}
+
+
+def dijkstra(graph, node):
+    costs = {node: math.inf for node in graph}
+    costs[node] = 0
+    parents = {node: None for node in graph}
+    queue = [(0, node)]
+
+    while queue:
+        current_cost, current_node = heapq.heappop(queue)
+
+        for next_node, weight in graph[current_node].items():
+            new_cost = current_cost + weight
+            if new_cost < costs[next_node]:
+                costs[next_node] = new_cost
+                parents[next_node] = current_node
+                heapq.heappush(queue, (new_cost, next_node))
+    return costs, parents
+
+
+costs, parents = dijkstra(graph, "start")
+print(f"lowest cost route: {costs['fin']}")

chapter9/with_heap/ex171c.py

@@ -0,0 +1,37 @@
+import heapq
+import logging
+import math
+
+logging.basicConfig(level=logging.DEBUG)
+logger = logging.getLogger(__name__)
+
+graph = {
+    "start": {"a": 2, "b": 2},
+    "a": {"b": 2},
+    "b": {"c": 2, "fin": 2},
+    "c": {"fin": 2},
+    "fin": {},
+}
+
+
+def dijkstra(graph, node):
+    costs = {node: math.inf for node in graph}
+    costs[node] = 0
+    parents = {node: None for node in graph}
+    queue = [(0, node)]
+
+    while queue:
+        current_cost, current_node = heapq.heappop(queue)
+
+        for next_node, weight in graph[current_node].items():
+            new_cost = current_cost + weight
+            if new_cost < costs[next_node]:
+                costs[next_node] = new_cost
+                parents[next_node] = current_node
+                heapq.heappush(queue, (new_cost, next_node))
+    return costs, parents
+
+
+costs, parents = dijkstra(graph, "start")
+
+print(f"lowest cost route: {costs['fin']}")