day5.py

#!/bin/python

# solution for https://adventofcode.com/2021/day/5

data = []
with open('day5.txt') as f:
    for line in f:
        data.append([tuple(map(int, c.split(','))) for c in line.strip().split(' -> ')])

def get_line_points(pair):
    yield '%s,%s' % pair[0]
    [[x1, y1], [x2, y2]] = pair
    while not (x1 == x2 and y1 == y2):
        if x1 < x2: x1 += 1
        if y1 < y2: y1 += 1
        if x1 > x2: x1 -= 1
        if y1 > y2: y1 -= 1
        yield '%s,%s' % (x1, y1)

# part 1 filter, comment out for part 2
data = filter(lambda c: c[0][0] == c[1][0] or c[0][1] == c[1][1], data)

point_groups = {}

for pair in data:
    for point in get_line_points(pair):
        if point not in point_groups:
            point_groups[point] = 0
        point_groups[point] += 1

high_risk_areas = list(filter(lambda v: v > 1, point_groups.values()))
print(len(high_risk_areas))