[Feature] Added depth first search for 2D graph.

Author: exterkamp

README.md

@@ -35,6 +35,8 @@ $ coverage report -m
 * [Breadth First Search](searches/breadth_first_search.py)
   * [2D Grid BFS](searches/breadth_first_search.py)
   * [Graph BFS](searches/breadth_first_search.py)
+* [Depth First Search](searches/depth_first_search.py)
+  * [2D Grid DFS](searches/depth_first_search.py)
 * [Finding Duplicates](searches/find_duplicates.py)
 * [Dijkstra's Pathfinding](searches/dijkstras.py)
 

searches/depth_first_search.py

@@ -0,0 +1,41 @@
+def depth_first_search(grid, start, target):
+    """
+    Search a 2d grid for a given target starting at start.
+
+    Args:
+        grid: the input grid as a List[List]
+        start: the start grid in format (x,y) zero index
+        target: the target value to find in the grid
+    Returns:
+        Coordinate of the target. Or None if cannot be found. 
+    """
+    height = len(grid)
+    if not height:
+        return None
+    width = len(grid[0])
+
+    x_start = start[0]
+    y_start = start[1]
+
+    # short circuit the start lookup
+    if grid[y_start][x_start] == target:
+        return (x_start, y_start)
+
+    visited = set()
+
+    stack = [(x_start, y_start)]
+    visited.add((x_start, y_start))
+    
+    while stack:
+        current = stack.pop()
+        
+        for coor in [(current[0], current[1]-1),(current[0]-1, current[1]),(current[0]+1, current[1]),(current[0], current[1]+1)]:
+            if coor[0] < 0 or coor[0] > width-1 or coor[1] < 0 or coor[1] > height-1:
+                continue
+            if grid[coor[1]][coor[0]] == target:
+                return coor
+            else:
+                if coor not in visited:
+                    stack.append(coor)
+                    visited.add(current)
+    return None

tests/test_2d_dfs.py

@@ -0,0 +1,37 @@
+import unittest
+from searches.depth_first_search import depth_first_search
+
+class TestBFS(unittest.TestCase):
+
+    def make_simple_grid(self):
+        return [
+            [1,0,3,4],
+            [5,6,2,6],
+            [8,8,1,3],
+        ]
+    
+    def make_complex_grid(self):
+        return [
+            [1,0,3,4,7,12,4,111],
+            [5,6,2,6,0,1,54,3],
+            [8,8,1,3,2,6,8,22],
+            [8,8,1,3,4,0,77,1],
+            [8,8,1,3,-1,4,2,9],
+        ]
+
+    def test_dfs_basic(self):
+        self.assertEqual((1,2), depth_first_search(self.make_simple_grid(), (3, 0), 8))
+
+    def test_find_farther_first(self):
+        self.assertEqual((3,2), depth_first_search(self.make_simple_grid(), (0, 2), 3))
+
+    def test_dfs_complex(self):
+        self.assertEqual((7,0), depth_first_search(self.make_complex_grid(), (7, 4), 111))
+
+        self.assertEqual((0,4), depth_first_search(self.make_complex_grid(), (0, 4), 8))
+
+    def test_dfs_empty(self):
+        self.assertEqual(None, depth_first_search([],(0,1),0))
+    
+    def test_dfs_not_found(self):
+        self.assertEqual(None, depth_first_search(self.make_simple_grid(), (0,0), -1))