4-9

4-9.py

@@ -0,0 +1,82 @@
+# -----------
+# User Instructions:
+# 
+# Modify the function search() so that it returns
+# a table of values called expand. This table
+# will keep track of which step each node was
+# expanded.
+#
+# For grading purposes, please leave the return
+# statement at the bottom.
+# ----------
+
+
+grid = [[0, 0, 1, 0, 0, 0],
+        [0, 0, 0, 0, 0, 0],
+        [0, 0, 1, 0, 1, 0],
+        [0, 0, 1, 0, 1, 0],
+        [0, 0, 1, 0, 1, 0]]
+
+init = [0, 0]
+goal = [len(grid)-1, len(grid[0])-1]
+
+delta = [[-1, 0 ], # go up
+         [ 0, -1], # go left
+         [ 1, 0 ], # go down
+         [ 0, 1 ]] # go right
+
+delta_name = ['^', '<', 'v', '>']
+
+cost = 1
+
+
+# ----------------------------------------
+# modify code below
+# ----------------------------------------
+
+def search():
+    count = 0
+    closed = [[0 for row in range(len(grid[0]))] for col in range(len(grid))]
+    closed[init[0]][init[1]] = 1
+    expand = [[-1 for row in range(len(grid[0]))] for col in range(len(grid))]
+    closed[init[0]][init[1]] = 0
+
+    x = init[0]
+    y = init[1]
+    g = 0
+
+    open = [[g, x, y]]
+
+    found = False  # flag that is set when search is complete
+    resign = False # flag set if we can't find expand
+
+    while not found and not resign:
+        if len(open) == 0:
+            resign = True
+        else:
+            open.sort()
+            open.reverse()
+            next = open.pop()
+            x = next[1]
+            y = next[2]
+            g = next[0]
+
+            if x == goal[0] and y == goal[1]:
+                found = True
+            else:
+                count += 1
+                for i in range(len(delta)):
+                    x2 = x + delta[i][0]
+                    y2 = y + delta[i][1]
+                    if x2 >= 0 and x2 < len(grid) and y2 >=0 and y2 < len(grid[0]):
+                        if closed[x2][y2] == 0 and grid[x2][y2] == 0:
+                            g2 = g + cost
+                            open.append([g2, x2, y2])
+                            closed[x2][y2] = 1
+                            expand[x2][y2] = count
+    return expand #Leave this line for grading purposes!
+
+
+
+print search()
+