This repository contains:
- Random Stack Overflow answers
- Short little scripts
- Homework calculations
- Testing language features, libraries, tools
- Hello worlds and exercises
- Challenges: vimgolf, project euler
Fun Examples:
Reimplementation of boost::algorithm::join in pure C++:
template <typename T, template<typename> typename IterType>
std::string join(
IterType<T> begin,
IterType<T> end,
std::string&& delimiter) {
auto first = *begin;
return std::accumulate(++begin, end,
std::to_string(first),
[&delimiter](std::string& a, T b) {
return a + delimiter + std::to_string(b);
});
}Y}Pf1R7 11<C-O>3j<CR>New te<C-N>.<CR><Esc>ZZ>>> slice s n = take (length s) $ drop n $ cycle s
>>> cyclicPerms s = map (slice s) [1..(length s)]
>>> cyclicPerms "abcde"
["bcdea","cdeab","deabc","eabcd","abcde"]import itertools
def snake(low, high):
return itertools.cycle(itertools.chain(
range(low, high + 1),
range(high, low - 1, -1)))
def shy(seq_func, iterable):
prev = None
for x in iterable:
if x != prev:
it = seq_func()
yield next(it)
def shy_snake(low, high, iterable):
"""d-d-doesss s-s-sssenpai noticesss me?"""
return shy(lambda: snake(low, high), iterable)
dirs = [1, 1, 1, 1, 2, 2, 2]
print(dirs)
print(list(itertools.islice(snake(1, 3), 7)))
print(list(shy_snake(1, 3, dirs)))Putnam Mathematical Competition numerical proofs:
# 2018 A-2
from itertools import chain, combinations
import numpy as np
np.set_printoptions(threshold=np.nan)
def powerset(iterable):
s = list(iterable)
ps = chain.from_iterable(combinations(s, r) for r in range(len(s) + 1))
ps = [x for x in ps if len(x) > 0] # exclude null set
return sorted(ps, key=lambda x: (len(x), *x))
def cartesian_self_product(a):
return np.meshgrid(a, a)
def I(a, b):
return (a & b) > 0
def encode_bitvector(xs, n, dtype):
enc = np.zeros((len(xs), n), dtype=np.uint8)
for i, x in enumerate(xs):
enc[i, x] = 1
bits = np.packbits(enc, axis=-1)
return bits.view(dtype)
def get_dtype(n):
return (
np.uint8 if n <= 8 else
np.uint16 if n <= 16 else
np.uint32 if n <= 32 else
np.uint64 if n <= 64 else None)
for n in range(2, 14):
dtype = get_dtype(n)
ps = powerset(range(n))
ps_enc = encode_bitvector(ps, n, dtype)
prod = cartesian_self_product(ps_enc)
M = I(*prod).astype(dtype)
det = int(np.linalg.det(M))
print(f'n={n} determinant: {det}')