feat(algs): add dfs alg

Author: jessicayung

algorithms/dfs.py

@@ -0,0 +1,42 @@
+"""
+Depth-first Search on a 2D grid
+
+Note: 'steps' indicates order of expansion, not distance from the source cell.
+
+Jessica Yung
+Jan 2018
+"""
+import numpy as np
+from queue import Queue
+from grid2d import Grid2D
+
+class DFS2D(Grid2D):
+
+    def __init__(self, grid_width, grid_height, visited=None):
+        Grid2D.__init__(self, grid_width, grid_height, visited)
+
+    def dfs(self, x, y, steps=0):
+        """Depth-First Search algorithm that visits every cell in a 2D grid.
+        """
+        if x >= self.grid_width or y >= self.grid_height:
+            return
+        if x < 0 or y < 0:
+            return
+        if self.visited[y][x]:
+            return
+
+        # Mark current cell as visited
+        self.visited[y][x] = True
+        self.steps_taken[y][x] = steps
+        steps += 1
+
+        # Visit every neighbouring cell
+        for cell in self.neighbour(x, y):
+            cellx = cell[0]
+            celly = cell[1]
+            self.dfs(cellx, celly, steps)
+
+dfs = DFS2D(4, 3)
+dfs.dfs(1,2)
+print("Order of expansion: \n", dfs.steps_taken)
+