This commit includes example tutorials and solutions for P4D2 2017. (#29)

- Added example P4 programs for ipv4_forwarding, mri, arp, calc
- Added python code to invoke compiler, start bmv2, run mininet
- Added solutions to above programs
- Added README files that describe exercises

P4D2_2017/utils/mininet/shortest_path.py

@@ -0,0 +1,78 @@
+class ShortestPath:
+
+    def __init__(self, edges=[]):
+        self.neighbors = {}
+        for edge in edges:
+            self.addEdge(*edge)
+
+    def addEdge(self, a, b):
+        if a not in self.neighbors: self.neighbors[a] = []
+        if b not in self.neighbors[a]: self.neighbors[a].append(b)
+
+        if b not in self.neighbors: self.neighbors[b] = []
+        if a not in self.neighbors[b]: self.neighbors[b].append(a)
+
+    def get(self, a, b, exclude=lambda node: False):
+        # Shortest path from a to b
+        return self._recPath(a, b, [], exclude)
+
+    def _recPath(self, a, b, visited, exclude):
+        if a == b: return [a]
+        new_visited = visited + [a]
+        paths = []
+        for neighbor in self.neighbors[a]:
+            if neighbor in new_visited: continue
+            if exclude(neighbor) and neighbor != b: continue
+            path = self._recPath(neighbor, b, new_visited, exclude)
+            if path: paths.append(path)
+
+        paths.sort(key=len)
+        return [a] + paths[0] if len(paths) else None
+
+if __name__ == '__main__':
+
+    edges = [
+            (1, 2),
+            (1, 3),
+            (1, 5),
+            (2, 4),
+            (3, 4),
+            (3, 5),
+            (3, 6),
+            (4, 6),
+            (5, 6),
+            (7, 8)
+
+    ]
+    sp = ShortestPath(edges)
+
+    assert sp.get(1, 1) == [1]
+    assert sp.get(2, 2) == [2]
+
+    assert sp.get(1, 2) == [1, 2]
+    assert sp.get(2, 1) == [2, 1]
+
+    assert sp.get(1, 3) == [1, 3]
+    assert sp.get(3, 1) == [3, 1]
+
+    assert sp.get(4, 6) == [4, 6]
+    assert sp.get(6, 4) == [6, 4]
+
+    assert sp.get(2, 6) == [2, 4, 6]
+    assert sp.get(6, 2) == [6, 4, 2]
+
+    assert sp.get(1, 6) in [[1, 3, 6], [1, 5, 6]]
+    assert sp.get(6, 1) in [[6, 3, 1], [6, 5, 1]]
+
+    assert sp.get(2, 5) == [2, 1, 5]
+    assert sp.get(5, 2) == [5, 1, 2]
+
+    assert sp.get(4, 5) in [[4, 3, 5], [4, 6, 5]]
+    assert sp.get(5, 4) in [[5, 3, 4], [6, 6, 4]]
+
+    assert sp.get(7, 8) == [7, 8]
+    assert sp.get(8, 7) == [8, 7]
+
+    assert sp.get(1, 7) == None
+    assert sp.get(7, 2) == None
+