FIRST OFF, DONT RESPOND UNLESS YOU CAN ACTUALLY HELP. IVE ASKED MANY VARIATIONS
ID: 3592582 • Letter: F
Question
FIRST OFF, DONT RESPOND UNLESS YOU CAN ACTUALLY HELP. IVE ASKED MANY VARIATIONS OF THIS SAME QUESTION WITH NO HELPFUL RESPONSES. Keep in mind that I am using the JES IDE and this is the only reason i can think why this code in python isnt producing the expected output. The output i am getting is this when i run spermutations(3) : my input typed in bottom window : >>> spermutations(3) Output produced in bottom window: <generator object at 0x3c>
Someone else ran it using a different IDE and it produced the desired/expected output but i am required to use JES. Can someone tell me what changes are required to make in the code i post at the end of this question to get the following output when i run spermutations(n) with n=3 and then n=4.
Permutations and sign of 3 items
The following is my Existing code (that produces the unusual/unwanted output). Im guessing the only cause for this is that it needs to be adapted for JES. PLEASE HELP:
from operator import itemgetter
DEBUG = False # like the built-in __debug__
def spermutations(n):
"""permutations by swapping. Yields: perm, sign"""
sign = 1
p = [[i, 0 if i == 0 else -1] # [num, direction]
for i in range(n)]
if DEBUG: print ' #', p
yield tuple(pp[0] for pp in p), sign
while any(pp[1] for pp in p): # moving
i1, (n1, d1) = max(((i, pp) for i, pp in enumerate(p) if pp[1]),
key=itemgetter(1))
sign *= -1
if d1 == -1:
# Swap down
i2 = i1 - 1
p[i1], p[i2] = p[i2], p[i1]
# If this causes the chosen element to reach the First or last
# position within the permutation, or if the next element in the
# same direction is larger than the chosen element:
if i2 == 0 or p[i2 - 1][0] > n1:
# The direction of the chosen element is set to zero
p[i2][1] = 0
elif d1 == 1:
# Swap up
i2 = i1 + 1
p[i1], p[i2] = p[i2], p[i1]
# If this causes the chosen element to reach the first or Last
# position within the permutation, or if the next element in the
# same direction is larger than the chosen element:
if i2 == n - 1 or p[i2 + 1][0] > n1:
# The direction of the chosen element is set to zero
p[i2][1] = 0
if DEBUG: print ' #', p
yield tuple(pp[0] for pp in p), sign
for i3, pp in enumerate(p):
n3, d3 = pp
if n3 > n1:
pp[1] = 1 if i3 < i2 else -1
if DEBUG: print ' # Set Moving'
if __name__ == '__main__':
from itertools import permutations
for n in (3, 4):
print ' Permutations and sign of %i items' % n
sp = set()
for i in spermutations(n):
sp.add(i[0])
print('Perm: %r Sign: %2i' % i)
#if DEBUG: raw_input('?')
# Test
p = set(permutations(range(n)))
assert sp == p, 'Two methods of generating permutations do not agree'
Explanation / Answer
def spermutations(n):
"""permutations by swapping. Yields: perm, sign"""
sign = 1
p = [[i, 0 if i == 0 else -1] # [num, direction]
for i in range(n)]
if DEBUG: print ' #', p
yield tuple(pp[0] for pp in p), sign
while any(pp[1] for pp in p): # moving
i1, (n1, d1) = max(((i, pp) for i, pp in enumerate(p) if pp[1]),
key=itemgetter(1))
sign *= -1
if d1 == -1:
# Swap down
i2 = i1 - 1
p[i1], p[i2] = p[i2], p[i1]
# If this causes the chosen element to reach the First or last
# position within the permutation, or if the next element in the
# same direction is larger than the chosen element:
if i2 == 0 or p[i2 - 1][0] > n1:
# The direction of the chosen element is set to zero
p[i2][1] = 0
elif d1 == 1:
# Swap up
i2 = i1 + 1
p[i1], p[i2] = p[i2], p[i1]
# If this causes the chosen element to reach the first or Last
# position within the permutation, or if the next element in the
# same direction is larger than the chosen element:
if i2 == n - 1 or p[i2 + 1][0] > n1:
# The direction of the chosen element is set to zero
p[i2][1] = 0
if DEBUG: print ' #', p
yield tuple(pp[0] for pp in p), sign
for i3, pp in enumerate(p):
n3, d3 = pp
if n3 > n1:
pp[1] = 1 if i3 < i2 else -1
if DEBUG: print ' # Set Moving'
if __name__ == '__main__':
from itertools import permutations
for n in (3, 4):
print ' Permutations and sign of %i items' % n
sp = set()
for i in spermutations(n):
sp.add(i[0])
print('Perm: %r Sign: %2i' % i)
#if DEBUG: raw_input('?')
# Test
p = set(permutations(range(n)))
assert sp == p, 'Two methods of generating permutations do not agree'
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