advent/2018/11.py

class Grid:
    def __init__(self, serial):
        self.serial = serial
        self.cells = []
        self.populate()
        
    def populate(self):
        for y in range(1, 301):
            self.cells.append([])
            for x in range(1, 301):
                self.cells[y - 1].append([])
                power = self.cell_power(x, y)
                self.set(x, y, power)

    def get(self, x, y):
        return self.cells[y - 1][x - 1]

    def set(self, x, y, value):
        self.cells[y - 1][x - 1] = value

    def cell_power(self, x, y):
        rack = x + 10
        p = (rack * y + self.serial) * rack
        p = (p // 100) % 10 # keep only hundreds digit
        return p - 5


class Cursor:
    def __init__(self, parent_grid, cursor_size):
        self.grid = parent_grid
        self.size = cursor_size
        self.x = self.y = 1
        self.total_power = self.calc_power()

    def step(self, direction):
        if direction in ('right', 'left'):
            axis = 'vertical'
            delta_x, delta_y = 1, 0
        elif direction in ('up', 'down'):
            axis = 'horizontal'
            delta_x, delta_y = 0, 1

        if direction in ('right', 'down'):
            offset_new, offset_old = self.size, 0
        elif direction in ('left', 'up'):
            offset_new, offset_old = -1, self.size - 1
            delta_x, delta_y = delta_x * -1, delta_y * -1

        new_points = self.get_row(offset_new, axis)
        old_points = self.get_row(offset_old, axis)
        self.total_power += sum(new_points)
        self.total_power -= sum(old_points)
        self.x, self.y = self.x + delta_x, self.y + delta_y

    def get_row(self, delta, axis):
        points = []
        if axis == 'vertical':
            for y in range(self.y, self.y + self.size):
                points.append(self.grid.get(self.x + delta, y))
        elif axis == 'horizontal':
            for x in range(self.x, self.x + self.size):
                points.append(self.grid.get(x, self.y + delta))
        return points

    def jump(self, x, y):
        self.x = x
        self.y = y
        self.total_power = self.calc_power()

    def calc_power(self):
        total = 0
        for y in range(self.size):
            for x in range(self.size):
                total += self.grid.get(self.x + x, self.y + y)
        return total

    def find_max(self):
        coords, max_power = (0, 0), 0
        prev_dir = 'down'
        while True:
            if self.total_power > max_power:
                coords, max_power = (self.x, self.y), self.total_power

            if self.x in (1, 301 - self.size) and prev_dir != 'down': # cursor is at edge of grid
                direction = 'down'
            elif self.y % 2 == 0: # go left on even lines
                direction = 'left'
            else: # go right on odd lines
                direction = 'right'
            prev_dir = direction

            try:
                self.step(direction)
            except IndexError:
                break

        return coords, max_power


grid = Grid(7857)
cursor = Cursor(grid, 3)
coords, max_power = cursor.find_max()
print(f'Part 1: {coords[0]},{coords[1]}, ({max_power})\n')

coords = max_power = grid_size = 0
for s in range(1, 301):
    cursor = Cursor(grid, s)
    c, m = cursor.find_max()
    if m > max_power:
        coords, max_power, grid_size = c, m, s

print(f'Part 2: {coords[0]},{coords[1]},{grid_size} ({max_power})\n')