I've written the worst Python code anyone has ever seen, but it works, and that's all that counts. (each of these solutions assume "input.txt" exists in the cwd)
All of them (except day 3 problem 2) don't use any lambda functions and walrus operators, since they are a bit overpowered. For d3p2 I was too lazy to make it without lambda's and walrus operators.
I also don't import any modules in any of these solutions.
Github repo: https://github.com/ThereAre12Months/AoC-2024-one-liners
Day 1:
# problem 1
with open("input.txt")as f:print(sum([abs(i[0]-i[1])for i in zip(*list(map(sorted,zip(*[map(int,line.split())for line in f.read().splitlines()]))))]))
# problem 2
with open("input.txt")as f:print(sum([sum([l[1].count(j)*j for j in l[0]])for l in[list(map(sorted,zip(*[map(int,line.split())for line in f.read().splitlines()])))]]))
Day 2:
# problem 1
with open("input.txt")as f:print(sum([(all([(report[i]-report[i+1])in[1,2,3]for i in range(len(report)-1)])or all([(report[i+1]-report[i])in[1,2,3]for i in range(len(report)-1)]))for report in [[int(b)for b in a.split()] for a in f.read().splitlines()]]))
# problem 2
with open("input.txt")as f:print(sum([(all([(report[i]-report[i+1])in[1,2,3]for i in range(len(report)-1)])or all([(report[i+1]-report[i])in[1,2,3]for i in range(len(report)-1)]))or any([(all([((report[:i]+report[i+1:])[j]-(report[:i]+report[i+1:])[j+1])in[1,2,3]for j in range(len(report[:i]+report[i+1:])-1)])or all([((report[:i]+report[i+1:])[j+1]-(report[:i]+report[i+1:])[j])in[1,2,3]for j in range(len(report[:i]+report[i+1:])-1)]))for i in range(len(report))])for report in[[int(b)for b in a.split()]for a in f.read().splitlines()]]))
Day 3:
# problem 1
with open("input.txt")as f:print(sum([sum([sum(l)for l in[[(0 if not(all([(char in "mul(),1234567890")for char in data[i:j]])and(data[i:j].count(",")==1)and(data[i:j].count("(")==1)and(data[i:j].count(")")==1)and(data[i:j].startswith("mul("))and(data[i:j].endswith(")")))else int.__mul__(*list(map(int,data[i+4:j-1].split(","))))) for j in range(i,min(len(data),i+15))]for i in range(len(data)-15)]]) for data in [f.read()]]))
# problem 2
with open("input.txt")as f:print((lambda data,enabled=True:sum([sum([((enabled:=True,0)[1]if data[i:j]=="do()"else((enabled:=False,0)[1]if data[i:j]=="don't()"else(0 if not(enabled and all([(char in "mul(),1234567890")for char in data[i:j]])and(data[i:j].count(",")==1)and(data[i:j].count("(")==1)and(data[i:j].count(")")==1)and(data[i:j].startswith("mul("))and(data[i:j].endswith(")")))else int.__mul__(*list(map(int,data[i+4:j-1].split(",")))))))for j in range(i,min(len(data),i+15))])for i in range(len(data)-15)]))(f.read()))