Two sum: Difference between revisions
Content added Content deleted
(→{{header|OCaml}}: explanations) |
(→{{header|Python}}: Updated primitives and output, pylinted for Python 3, added {Works with}) |
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Line 1,657:
or, in terms of '''itertools.product''':
{{Works with|Python|3.7}}
<lang python>'''Finding two integers that sum to a target value.'''
# sumTwo :: [Int] ->
def sumTwo(
'''All the pairs of integers in xs which
(fst(x), fst(y)) for (x, y) in (▼
def go(n):
product(ixs, ixs[1:])▼
▲ (fst(x), fst(y)) for (x, y) in (
▲ product(ixs, ixs[1:])
) if fst(x) < fst(y) and n == snd(x) + snd(y)
return lambda n: go(n)
Line 1,675 ⟶ 1,682:
# main :: IO ()
def main():
'''Tests'''
▲ print (
xs
▲ )
print(
fTable(
'The indices of any two integers drawn from ' + repr(xs) +
'\nthat sum to a given value:\n'
)(str)(
lambda x: str(x) + ' = ' + ', '.join(
['(' + str(xs[a]) + ' + ' + str(xs[b]) + ')' for a, b in x]
) if x else '(none)'
)(
sumTwo(xs)
)(enumFromTo(10)(25))
)
# GENERIC -------------------------------------------------
# enumFromTo :: (Int, Int) -> [Int]
def enumFromTo(m):
'''Integer enumeration from m to n.'''
return lambda n: list(range(m, 1 + n))
# fst :: (a, b) -> a
def fst(tpl):
'''First member of a pair.'''
return tpl[0]
Line 1,691 ⟶ 1,716:
# snd :: (a, b) -> b
def snd(tpl):
'''Second member of a pair.'''
return tpl[1]
# DISPLAY -------------------------------------------------
# fTable :: String -> (a -> String) ->
# (b -> String) -> (a -> b) -> [a] -> String
def fTable(s):
'''Heading -> x display function -> fx display function ->
f -> xs -> tabular string.
'''
def go(xShow, fxShow, f, xs):
ys = [xShow(x) for x in xs]
w = max(map(len, ys))
return s + '\n' + '\n'.join(map(
lambda x, y: y.rjust(w, ' ') + ' -> ' + fxShow(f(x)),
xs, ys
))
return lambda xShow: lambda fxShow: lambda f: lambda xs: go(
xShow, fxShow, f, xs
)
# MAIN ---
if __name__ == '__main__':
main()</lang>
{{Out}}
<pre>The indices of any two integers drawn from [0, 2, 11, 19, 90, 10]
<pre>[(1, 3), (2, 5)]▼
that sum to a given value:
10 -> [(0, 5)] = (0 + 10)
11 -> [(0, 2)] = (0 + 11)
13 -> [(1, 2)] = (2 + 11)
14 -> (none)
15 -> (none)
16 -> (none)
17 -> (none)
18 -> (none)
19 -> [(0, 3)] = (0 + 19)
20 -> (none)
21 -> [(1, 3), (2, 5)] = (2 + 19), (11 + 10)
22 -> (none)
23 -> (none)
24 -> (none)
25 -> (none)</pre>
or, a little more parsimoniously (not generating the entire cartesian product), in terms of '''concatMap''':
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