Add example for distributing a Breadth First Search (#246)

* Add example for distributing a Breadth First Search

* Remove explorer decorator

examples/breadth_first_search_example.py

@@ -0,0 +1,67 @@
+from os import path
+import sys
+# Append to path so that this script can access the dipla package
+sys.path.append(path.abspath('../dipla'))
+
+from dipla.api import Dipla
+
+@Dipla.scoped_distributable(count=4)
+def bfs(grid, index, count):
+    from queue import Queue
+    q = Queue()
+    # Start in the center of the grid
+    q.put((len(grid)//2, len(grid)//2))
+    seen = set()
+    ans = []
+
+    # Split the grid into 4 quadrants, and calculate the bounds of each
+    bounds = [(0, 0), (1, 0), (0, 1), (1, 1)]
+    half_grid = len(grid)//2
+    min_x = bounds[index][0] * half_grid
+    min_y = bounds[index][1] * half_grid
+    max_x = min_x + half_grid
+    max_y = min_y + half_grid
+
+    # Standard breadth first search
+    while not q.empty():
+        popped = q.get()
+        directions = [(1, 0), (-1, 0), (0, 1),  (0, -1)]
+        for xy in directions:
+          newx = popped[0] + xy[0]
+          newy = popped[1] + xy[1]      
+
+          if newx < min_x or newx > max_x or newy < min_y or newy > max_y:
+              continue
+          new = (newx, newy)
+          if new in seen:
+              continue
+          if grid[new[1]][new[0]] == 2:
+              continue
+          if grid[new[1]][new[0]] == 1:
+              ans.append(new)
+          seen.add(new)
+          q.put(new)
+    return ans
+
+grid = [
+    [1, 0, 2, 2, 0, 0, 0],
+    [2, 0, 2, 2, 0, 0, 1],
+    [0, 0, 0, 0, 0, 0, 0],
+    [2, 2, 2, 0, 0, 0, 0],
+    [0, 0, 2, 0, 0, 2, 0],
+    [1, 0, 2, 0, 2, 1, 0],
+    [0, 0, 0, 0, 0, 0, 0]
+]
+
+# Apply a distributable function to the stream of values from
+# the above source
+bfs_result = Dipla.apply_distributable(bfs, [[grid]])
+
+out = Dipla.get(bfs_result)
+
+u = []
+for y in out:
+    u += [(x[0], x[1]) for x in y]
+
+for o in set(u):
+   print(o)