#!/usr/bin/env python
# coding: utf-8

# # Puzzle 2 of AoC 2025
# Author: Victoria Ramírez López
# 
# Date: Dec 4, 2025

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import numpy as np
from scipy.signal import convolve2d


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# Read input file

paper_roll_grid = open('paper_roll_grid.txt', mode ='r') # Open in 'read only' mode
grid = paper_roll_grid.readlines()
grid = [line.strip('\n') for line in grid]


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# Find roll papers accessible by fork lift

total_accessible_rolls = 1
total_removed_rolls = 0

 # Turn grid to boolean matrix 
bool_grid = create_boolean_grid(grid)
bool_grid_np = np.array(bool_grid) # Convert into numpy array

# For part 1
accessible_rolls = find_accessible_rolls(bool_grid_np)
total_accessible_rolls = accessible_rolls.sum()
print('Part 1 answer: ', total_accessible_rolls)

# For part 2
while total_accessible_rolls >= 1:
    accessible_rolls = find_accessible_rolls(bool_grid_np)
    total_accessible_rolls = accessible_rolls.sum()
    bool_grid_np = remove_accessible_rolls(bool_grid_np,accessible_rolls)
    total_removed_rolls = total_removed_rolls + total_accessible_rolls
    
print('Part 2 answer:', total_removed_rolls)


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def find_accessible_rolls(bool_grid_np):
    # This function finds the number of rolls that can be 
    # accessed by forklift
    # input: grid = [[String]]
    # output: sum_accessible_rolls = int

    # Add padding
    bool_grid_padded = np.pad(bool_grid_np, 1, mode='constant') 

    # Calculate how many rolls surround each roll
    convolution = convolve2d(bool_grid_padded, 
                                    [[1,1,1],[1,0,1],[1,1,1]], mode='same')
    convolution = convolution[1:-1,1:-1] # Remove padding

    # Determine how many rolls are reachable
    accessible_rolls = bool_grid_np & (convolution < 4)

    return accessible_rolls


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def remove_accessible_rolls(bool_grid_np, accessible_rolls):
    # This function removes the number of rolls that can be 
    # accessed by forklift
    # input: accessible_rolls = numpy array
    # output: updated_grid = numpy array
    
    updated_grid = np.logical_not(accessible_rolls) & bool_grid_np

    return(updated_grid)    


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def create_boolean_grid(grid):
    # This function turns the original grid to a matrix where
    # '@' is 1 and '.' is 0
    # input: grid = [String]
    # output: boolean_grid = [int]
    
    boolean_grid = []
    
    for row in grid:
        boolean_row = [1 if x == '@' else 0 for x in row]
        boolean_grid.append(boolean_row)

    return boolean_grid


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