Created
December 17, 2010 22:18
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어떤 수 구하기 (Python) by jong10
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# problem: http://club.filltong.net/codingdojo/27611 | |
# coded by jong10 | |
import unittest | |
# infix to prefix(s-expression) | |
# modified from http://news.ycombinator.com/item?id=284954 | |
def parse(s): | |
for operator in ["+-", "*/"]: | |
depth = 0 | |
for p in xrange(len(s) - 1, -1, -1): | |
if s[p] == ')': depth += 1 | |
if s[p] == '(': depth -= 1 | |
if not depth and s[p] in operator: | |
return (s[p], parse(s[:p]), parse(s[p+1:])) | |
s = s.strip() | |
if s[0] == '(': | |
return parse(s[1:-1]) | |
return s | |
# s-expression has the '_' ? | |
def has_x(expr): | |
if getattr(expr, '__iter__', False): | |
return reduce(lambda x, y: x + y > 0, (has_x(e) for e in expr)) | |
else: | |
return expr == '_' | |
# evaluate the s-expression without '_' | |
def evaluate(e): | |
if getattr(e, '__iter__', False): | |
return eval("%s%s%s" % (evaluate(e[1]), e[0], evaluate(e[2]))) | |
else: | |
return e | |
# reverse of operator | |
REVERSE = {'+': '-', '-': '+', '*': '/', '/': '*'} | |
# find number '_' of equation | |
def find_number(expr): | |
l, r = (parse(x) for x in expr.split('=')) | |
if has_x(r): | |
l, r = r, l # swap | |
r = evaluate(r) | |
while len(l) > 1 or len(r) > 1: | |
if l == '_': | |
break | |
op = REVERSE[l[0]] | |
if l[0] in '+*': | |
if has_x(l[2]): | |
move, other = 1, 2 | |
else: | |
move, other = 2, 1 | |
e = (op, r, l[move]) | |
l, r = l[other], str(evaluate(e)) | |
else: | |
move, other = 2, 1 | |
e = (op, r, l[move]) | |
if has_x(l[move]): | |
l, r = str(evaluate(l[other])), e | |
l, r = r, l | |
else: | |
l, r = l[other], str(evaluate(e)) | |
return eval(r) | |
# testcase | |
class TestFindNumber(unittest.TestCase): | |
def test_find_number(self): | |
self.assertEqual(find_number("_ + 2 = 12"), 10) | |
self.assertEqual(find_number("( _ * 2 ) + 10 = 20"), 5) | |
self.assertEqual(find_number("(3 + _) / 3 + 4 = 10"), 15) | |
self.assertEqual(find_number("3 - _ = 10"), -7) | |
self.assertEqual(find_number("3 - 103 = _ / 10 + 4"), -1040) | |
self.assertEqual(find_number("10 = _"), 10) | |
self.assertEqual(find_number("_ + 3.14 = 5.1234"), 1.9834) | |
if __name__ == '__main__': | |
unittest.main() |
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