Advent of Code 2024 Day 4

Author

Nathan Moore

— Day 4: Ceres Search —

We are doing a word search for XMAS

Take a look at the little Elf’s word search. How many times does XMAS appear?

import numpy as np 

with open('data-2024-04.txt', 'r') as f:
    inp = f.read().splitlines()

# 140 x 140
# len(inp)
# len(inp[0])

xx = [list(x) for x in inp]

grid = np.array(xx)

# grid[1:10]

Words have to start with X, then we have to search in possible directions.

x_count = 0

for i in range(len(inp)): 
    for j in range(len(inp[0])): 
        # print(grid[i,j])
        if grid[i,j] == 'X': 
            # west
            if ''.join(grid[i,j-3:j+1]) == 'SAMX': 
                x_count += 1
            # east
            if ''.join(grid[i,j:j+4]) == 'XMAS':
                x_count += 1
            # north 
            if ''.join(grid[i-3:i+1,j]) == 'SAMX':
                x_count += 1
            # south
            if ''.join(grid[i:i+4,j]) == 'XMAS':
                x_count += 1
            # northwest
            if i < 3 or j < 3: 
                pass
            elif (grid[i,j] + grid[i-1,j-1] + 
                  grid[i-2,j-2] + grid[i-3,j-3]) == 'XMAS':
                x_count += 1
            # northeast
            if i < 3 or j > 136: 
                pass
            elif (grid[i,j] + grid[i-1,j+1] + 
                  grid[i-2,j+2] + grid[i-3,j+3]) == 'XMAS':
                x_count += 1
            # southwest
            if i > 136 or j < 3: 
                pass
            elif (grid[i,j] + grid[i+1,j-1] + 
                  grid[i+2,j-2] + grid[i+3,j-3]) == 'XMAS':
                x_count += 1
            # southeast
            if i > 136 or j > 136: 
                pass
            elif (grid[i,j] + grid[i+1,j+1] + 
                  grid[i+2,j+2] + grid[i+3,j+3]) == 'XMAS':
                x_count += 1

x_count

# 2460 too low
# fix a spelling mistake in north check
# 2646

— Part Two —

oh, actually, we are looking for X-MAS i.e. two MAS in a X shape.

Flip the word search from the instructions back over to the word search side and try again. How many times does an X-MAS appear?

x_count = 0

for i in range(1,len(inp)-1): 
    for j in range(1,len(inp[0])-1): 
        # this time we are looking for A
        # but it is also symmetrical so we can not be in first or last
        if grid[i,j] == 'A':
            # if any of the surrounds are X then we don't have a thing
            if (grid[i-1,j-1] == 'X' or grid[i-1,j+1] == 'X' or
                grid[i+1,j-1] == 'X' or grid[i+1,j+1] == 'X'):
                    pass
            # M over S
            elif (grid[i-1,j-1] == 'M' and grid[i-1,j+1] == 'M' and
                  grid[i+1,j-1] == 'S' and grid[i+1,j+1] == 'S'):
                x_count += 1
            # S over M
            elif (grid[i-1,j-1] == 'S' and grid[i-1,j+1] == 'S' and
                  grid[i+1,j-1] == 'M' and grid[i+1,j+1] == 'M'):
                x_count += 1
            # M then S
            elif (grid[i-1,j-1] == 'M' and grid[i-1,j+1] == 'S' and
                  grid[i+1,j-1] == 'M' and grid[i+1,j+1] == 'S'):
                x_count += 1
            # S then M
            elif (grid[i-1,j-1] == 'S' and grid[i-1,j+1] == 'M' and
                  grid[i+1,j-1] == 'S' and grid[i+1,j+1] == 'M'):
                x_count += 1
            
            
# 4947 A in the grid
x_count

# 3115 too high
# fix the typo making sure we use and
# 2000