Can this implementation of natural merge be improved?
The code bellow is my implementation for the natural merge exercise in Robert Sedgwick's Algorithms book:
Write a version of bottom-up mergesort that takes advantage of order
in the array by proceeding as follows each time it needs to find two
arrays to merge: find a sorted subarray (by incrementing a pointer
until finding an entry that is smaller than its predecessor in the
array), then find the next, then merge them.
def merge(a, lo, mi, hi):
aux_lo = deque(a[lo:mi])
aux_hi = deque(a[mi:hi])
# this takes more space than allowed
for i in range(lo, hi):
if len(aux_lo) and len(aux_hi):
a[i] = aux_lo.popleft() if aux_lo[0] < aux_hi[0] else aux_hi.popleft()
elif len(aux_lo) or len(aux_hi):
a[i] = aux_lo.popleft() if aux_lo else aux_hi.popleft()
def find_next_stop(a, start):
if start >= len(a)-1:
return start
stop = start + 1
if a[start] < a[stop]:
while(stop<len(a)-1 and a[stop] <= a[stop+1]):
stop += 1
else:
while(stop<len(a)-1 and a[stop] >= a[stop+1]):
stop += 1
_stop = stop
while(start<_stop):
a[_stop], a[start] = a[start], a[_stop]
start += 1
_stop -= 1
return stop
def natural_merge(a):
lo = hi = 0
while(True):
lo = hi
mi = find_next_stop(a, lo)
if lo == 0 and mi == len(a) - 1:
return
hi = find_next_stop(a, mi)
if mi == hi == len(a)-1:
lo = hi = 0
continue
merge(a, lo, mi, hi)
I take this anwser as a referenced.
python algorithm python-3.x mergesort genetic-algorithm
asked 21 mins ago
lerner
1615
add a comment |
The code bellow is my implementation for the natural merge exercise in Robert Sedgwick's Algorithms book:
Write a version of bottom-up mergesort that takes advantage of order
in the array by proceeding as follows each time it needs to find two
arrays to merge: find a sorted subarray (by incrementing a pointer
until finding an entry that is smaller than its predecessor in the
array), then find the next, then merge them.
def merge(a, lo, mi, hi):
aux_lo = deque(a[lo:mi])
aux_hi = deque(a[mi:hi])
# this takes more space than allowed
for i in range(lo, hi):
if len(aux_lo) and len(aux_hi):
a[i] = aux_lo.popleft() if aux_lo[0] < aux_hi[0] else aux_hi.popleft()
elif len(aux_lo) or len(aux_hi):
a[i] = aux_lo.popleft() if aux_lo else aux_hi.popleft()
def find_next_stop(a, start):
if start >= len(a)-1:
return start
stop = start + 1
if a[start] < a[stop]:
while(stop<len(a)-1 and a[stop] <= a[stop+1]):
stop += 1
else:
while(stop<len(a)-1 and a[stop] >= a[stop+1]):
stop += 1
_stop = stop
while(start<_stop):
a[_stop], a[start] = a[start], a[_stop]
start += 1
_stop -= 1
return stop
def natural_merge(a):
lo = hi = 0
while(True):
lo = hi
mi = find_next_stop(a, lo)
if lo == 0 and mi == len(a) - 1:
return
hi = find_next_stop(a, mi)
if mi == hi == len(a)-1:
lo = hi = 0
continue
merge(a, lo, mi, hi)
I take this anwser as a referenced.
python algorithm python-3.x mergesort genetic-algorithm
asked 21 mins ago
lerner
1615
Add docstrings and typed arguments. Otherwise it's not bad
– Reinderien
13 mins ago
A pity the code presented is uncommented but for a crypticthis takes more space than allowed- extra constraint(s)? (There's more than one error inI take this anwser as a referenced..)
– greybeard
4 mins ago
add a comment |
The code bellow is my implementation for the natural merge exercise in Robert Sedgwick's Algorithms book:
Write a version of bottom-up mergesort that takes advantage of order
in the array by proceeding as follows each time it needs to find two
arrays to merge: find a sorted subarray (by incrementing a pointer
until finding an entry that is smaller than its predecessor in the
array), then find the next, then merge them.
def merge(a, lo, mi, hi):
aux_lo = deque(a[lo:mi])
aux_hi = deque(a[mi:hi])
# this takes more space than allowed
for i in range(lo, hi):
if len(aux_lo) and len(aux_hi):
a[i] = aux_lo.popleft() if aux_lo[0] < aux_hi[0] else aux_hi.popleft()
elif len(aux_lo) or len(aux_hi):
a[i] = aux_lo.popleft() if aux_lo else aux_hi.popleft()
def find_next_stop(a, start):
if start >= len(a)-1:
return start
stop = start + 1
if a[start] < a[stop]:
while(stop<len(a)-1 and a[stop] <= a[stop+1]):
stop += 1
else:
while(stop<len(a)-1 and a[stop] >= a[stop+1]):
stop += 1
_stop = stop
while(start<_stop):
a[_stop], a[start] = a[start], a[_stop]
start += 1
_stop -= 1
return stop
def natural_merge(a):
lo = hi = 0
while(True):
lo = hi
mi = find_next_stop(a, lo)
if lo == 0 and mi == len(a) - 1:
return
hi = find_next_stop(a, mi)
if mi == hi == len(a)-1:
lo = hi = 0
continue
merge(a, lo, mi, hi)
I take this anwser as a referenced.
python algorithm python-3.x mergesort genetic-algorithm
asked 21 mins ago
lerner
1615
The code bellow is my implementation for the natural merge exercise in Robert Sedgwick's Algorithms book:
Write a version of bottom-up mergesort that takes advantage of order
in the array by proceeding as follows each time it needs to find two
arrays to merge: find a sorted subarray (by incrementing a pointer
until finding an entry that is smaller than its predecessor in the
array), then find the next, then merge them.
def merge(a, lo, mi, hi):
aux_lo = deque(a[lo:mi])
aux_hi = deque(a[mi:hi])
# this takes more space than allowed
for i in range(lo, hi):
if len(aux_lo) and len(aux_hi):
a[i] = aux_lo.popleft() if aux_lo[0] < aux_hi[0] else aux_hi.popleft()
elif len(aux_lo) or len(aux_hi):
a[i] = aux_lo.popleft() if aux_lo else aux_hi.popleft()
def find_next_stop(a, start):
if start >= len(a)-1:
return start
stop = start + 1
if a[start] < a[stop]:
while(stop<len(a)-1 and a[stop] <= a[stop+1]):
stop += 1
else:
while(stop<len(a)-1 and a[stop] >= a[stop+1]):
stop += 1
_stop = stop
while(start<_stop):
a[_stop], a[start] = a[start], a[_stop]
start += 1
_stop -= 1
return stop
def natural_merge(a):
lo = hi = 0
while(True):
lo = hi
mi = find_next_stop(a, lo)
if lo == 0 and mi == len(a) - 1:
return
hi = find_next_stop(a, mi)
if mi == hi == len(a)-1:
lo = hi = 0
continue
merge(a, lo, mi, hi)
I take this anwser as a referenced.
python algorithm python-3.x mergesort genetic-algorithm
python algorithm python-3.x mergesort genetic-algorithm
asked 21 mins ago
lerner
1615
asked 21 mins ago
lerner
1615
asked 21 mins ago
lerner
1615
asked 21 mins ago
lerner
1615
asked 21 mins ago
lerner
1615
1615
Add docstrings and typed arguments. Otherwise it's not bad
– Reinderien
13 mins ago
A pity the code presented is uncommented but for a crypticthis takes more space than allowed- extra constraint(s)? (There's more than one error inI take this anwser as a referenced..)
– greybeard
4 mins ago
add a comment |
Add docstrings and typed arguments. Otherwise it's not bad
– Reinderien
13 mins ago
A pity the code presented is uncommented but for a crypticthis takes more space than allowed- extra constraint(s)? (There's more than one error inI take this anwser as a referenced..)
– greybeard
4 mins ago
Add docstrings and typed arguments. Otherwise it's not bad
– Reinderien
13 mins ago
Add docstrings and typed arguments. Otherwise it's not bad
– Reinderien
13 mins ago
A pity the code presented is uncommented but for a cryptic
this takes more space than allowed - extra constraint(s)? (There's more than one error in I take this anwser as a referenced..)– greybeard
4 mins ago
A pity the code presented is uncommented but for a cryptic
this takes more space than allowed - extra constraint(s)? (There's more than one error in I take this anwser as a referenced..)– greybeard
4 mins ago
add a comment |
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Add docstrings and typed arguments. Otherwise it's not bad
– Reinderien
13 mins ago
A pity the code presented is uncommented but for a cryptic
this takes more space than allowed- extra constraint(s)? (There's more than one error inI take this anwser as a referenced..)– greybeard
4 mins ago