added distances_to_start_pos.py

Author: Pl4tt

dynamic_programming/distance_to_start_pos.py

@@ -0,0 +1,80 @@
+# 0 = empty field
+# -1 = wall
+# -2 = starting position
+
+# replace every 0 with the minimal distance to the starting position without going through a wall
+# You are allowed to go right, left, up and down. Diagonal moves are not allowed
+# if there is no possibility to reach a 0, just leave it as a 0
+
+# input:
+#   n by n (n == n)
+
+# example:
+# [-2, 0, 0, -1] -> [-2, 1, 2, -1]
+# [0, -1, 0, -1] -> [1, -1, 3, -1]
+
+arr = [
+    [0, -2, -1, 0],
+    [0, -1, 0, -1],
+    [0,  0, 0, -1],
+    [-1, -1, 0, 0]
+]
+sol = [
+    [1, -2, -1, 0],
+    [2, -1, 6, -1],
+    [3, 4, 5, -1],
+    [-1, -1, 6, 7]
+]
+
+
+def solve(arr: list[list[int]]) -> list[list[int]]:
+    """changes all zero's to the distance to the starting position (-2)
+    if they are reachable, the not reachable zero's stays as zero's.
+    The modified arr will also be returned."""
+    visited, start_pos = create_seq(arr)
+    
+    depth_search(arr, *start_pos, visited, 0)
+    return arr
+
+def depth_search(arr: list[list[int]], x: int, y: int, visited: list[list[bool]], depth: int=0) -> None:
+    """goes through all reachable zero's in the arr list and changes
+    it's value to the distance to the starting position"""
+    if arr[x][y] == 0:
+        arr[x][y] = depth
+
+    visited[x][y] = True
+    depth += 1
+    
+    if x+1 < len(arr) and not visited[x+1][y] and arr[x+1][y] == 0:
+        depth_search(arr, x+1, y, visited, depth)
+    if y+1 < len(arr[x]) and not visited[x][y+1] and arr[x][y+1] == 0:
+        depth_search(arr, x, y+1, visited, depth)
+    if y-1 >= 0 and not visited[x][y-1] and arr[x][y-1] == 0:
+        depth_search(arr, x, y-1, visited, depth)
+    if x-1 >= 0 and not visited[x-1][y] and arr[x-1][y] == 0:
+        depth_search(arr, x-1, y, visited, depth)
+
+def create_seq(arr: list) -> tuple[list[list[bool]], tuple[int]]:
+    """Returns a visited list with lists of booleans
+    and the starting position as a tuple"""
+    result = []
+    for x in range(len(arr)):
+        result.append([])
+        for y in range(len(arr[0])):
+            if arr[x][y] == -2:
+                result[x].append(True)
+                start = (x, y)
+            elif arr[x][y] == -1:
+                result[x].append(True)
+            else:
+                result[x].append(False)
+    
+    return result, start
+
+
+
+
+if __name__ == "__main__":
+    solve(arr)
+    print(arr)
+    print(sol == arr)