euler/python/e083.py

from functools import namedtuple
from lib_a_star import A_Star
from e081 import get_grid


def euler_083():
    Node = namedtuple("Node", ["row", "col"])

    def cost(grid):
        n_rows = len(grid)
        n_cols = len(grid[0])
        start_node = Node(0, 0)
        end_node = Node(n_rows - 1, n_cols - 1)

        def h(node):
            return (end_node.row - node.row) + (end_node.col - node.col)

        def d(current_node, next_node):
            return grid[next_node.row][next_node.col]

        def neighbors(node):
            neighbors = []
            # right neighbor
            if not node.col + 1 == n_cols:
                neighbors.append(Node(node.row, node.col + 1))
            # left neighbor
            if not node.col == 0:
                neighbors.append(Node(node.row, node.col - 1))
            # down neighbor
            if not node.row + 1 == n_rows:
                neighbors.append(Node(node.row + 1, node.col))
            # up neighbor
            if not node.row == 0:
                neighbors.append(Node(node.row - 1, node.col))
            return neighbors

        a = A_Star([start_node], [end_node], h, d, neighbors)
        return a.cost

    grid = [[131, 673, 234, 103, 18],
            [201, 96, 342, 965, 150],
            [630, 803, 746, 422, 111],
            [537, 699, 497, 121, 956],
            [805, 732, 524, 37, 331]]
    assert(cost(grid) == 2297)  # Example from problem statement.
    return cost(get_grid())


if __name__ == "__main__":
    print("e083.py: " + str(euler_083()))
    assert(euler_083() == 425185)