Add code snippets.

algorithms/snippets/grids.py

@@ -0,0 +1,65 @@
+"""
+Grid-traversal-related snippets.
+
+Assumptions:
+
+* Zero-based indexing.
+* When limits are asked for, the value given is 1 more than the last addressable
+  value for that dimension in the grid.
+"""
+
+def get_adjacent_8c(p, row_limit, col_limit):
+    """
+    Get the adjacent cells of the given point p assuming adjacency is 8-connected.
+    """
+    rows = [p[0]]
+    cols = [p[1]]
+
+    if p[0] == 0:
+        rows.append(p[0] + 1)
+    elif p[0] == (row_limit - 1):
+        rows.append(p[0] - 1)
+    else:
+        rows.extend([p[0] + 1, p[0] - 1])
+
+    if p[1] == 0:
+        cols.append(p[1] + 1)
+    elif p[1] == (col_limit - 1):
+        cols.append(p[1] - 1)
+    else:
+        cols.extend([p[1] + 1, p[1] - 1])
+
+    adjacent = []
+
+    for r in rows:
+        for c in cols:
+            adjacent.append((r, c))
+
+def get_adjacent_4c(p, row_limit, col_limi):
+    """
+    Get the adjacent cells of the given point p assuming adjacency is 8-connected.
+    """
+    rows = []
+    cols = []
+
+    if p[0] == 0:
+        rows.append(p[0] + 1)
+    elif p[0] == (row_limit - 1):
+        rows.append(p[0] - 1)
+    else:
+        rows.extend([p[0] + 1, p[0] - 1])
+
+    if p[1] == 0:
+        cols.append(p[1] + 1)
+    elif p[1] == (col_limit - 1):
+        cols.append(p[1] - 1)
+    else:
+        cols.extend([p[1] + 1, p[1] - 1])
+
+    adjacent = []
+
+    for r in rows:
+        adjacent.append((r, p[1]))
+
+    for c in cols:
+        adjacent.append((p[0], c))