euler/python/e082.py

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


def euler_082():
    Node = namedtuple("Node", ["row", "col"])

    def cost(grid):
        n_rows = len(grid)
        n_cols = len(grid[0])
        start_nodes = [Node(row, 0) for row in range(n_rows)]
        end_nodes = [Node(row, n_cols - 1) for row in range(n_rows)]

        def h(node):
            c_self = grid[node.row][node.col]
            c_steps = n_cols - node.col
            return c_self + c_steps

        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))
            # 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_nodes, end_nodes, 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) == 994)  # Example from problem statement.
    return cost(get_grid())


if __name__ == "__main__":
    print("e082.py: " + str(euler_082()))
    assert(euler_082() == 260324)