https://adventofcode.com/2023/day/6

day6.py

# ts, ds = [[int(i) for i in l.split()[1:]] for l in open(0).read().split('\n') if l] # part 1
ts, ds = [[int(i) for i in [''.join(l.split()[1:])]] for l in open(0).read().split('\n') if l] # part 2

def binary_search(f, l, r):
    while l < r:
        m = (l+r)//2
        if f(m):
            l = m+1
        else:
            r = m
    return l

ans = 1
for T, D in zip(ts, ds):
    f = lambda t: t*(T-t) - D
    argmax = binary_search(lambda t: f(t) < f(t+1), 0, T) # no calculus assumed
    sl = binary_search(lambda t: f(t) <= 0, 0, argmax)
    sr = binary_search(lambda t: f(t) > 0, argmax, T)
    ans *= sr-sl
print(ans)