Natural merge: mergesort that uses already sorted subarrays
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 reference.
python algorithm python-3.x sorting mergesort
edited 4 mins ago
200_success
128k15150412
asked 52 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 reference.
python algorithm python-3.x sorting mergesort
edited 4 mins ago
200_success
128k15150412
asked 52 mins ago
lerner
1615
Add docstrings and typed arguments. Otherwise it's not bad
– Reinderien
43 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
35 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 reference.
python algorithm python-3.x sorting mergesort
edited 4 mins ago
200_success
128k15150412
asked 52 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 reference.
python algorithm python-3.x sorting mergesort
python algorithm python-3.x sorting mergesort
edited 4 mins ago
200_success
128k15150412
asked 52 mins ago
lerner
1615
edited 4 mins ago
200_success
128k15150412
asked 52 mins ago
lerner
1615
edited 4 mins ago
200_success
128k15150412
edited 4 mins ago
200_success
128k15150412
edited 4 mins ago
200_success
128k15150412
128k15150412
asked 52 mins ago
lerner
1615
asked 52 mins ago
lerner
1615
asked 52 mins ago
lerner
1615
1615
Add docstrings and typed arguments. Otherwise it's not bad
– Reinderien
43 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
35 mins ago
add a comment |
Add docstrings and typed arguments. Otherwise it's not bad
– Reinderien
43 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
35 mins ago
Add docstrings and typed arguments. Otherwise it's not bad
– Reinderien
43 mins ago
Add docstrings and typed arguments. Otherwise it's not bad
– Reinderien
43 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
35 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
35 mins ago
add a comment |
active
oldest
votes
Your Answer
StackExchange.ifUsing("editor", function () {
return StackExchange.using("mathjaxEditing", function () {
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix) {
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["\$", "\$"]]);
});
});
}, "mathjax-editing");
StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "196"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fcodereview.stackexchange.com%2fquestions%2f210315%2fnatural-merge-mergesort-that-uses-already-sorted-subarrays%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
active
oldest
votes
active
oldest
votes
active
oldest
votes
active
oldest
votes
Thanks for contributing an answer to Code Review Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
Use MathJax to format equations. MathJax reference.
To learn more, see our tips on writing great answers.
Some of your past answers have not been well-received, and you're in danger of being blocked from answering.
Please pay close attention to the following guidance:
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fcodereview.stackexchange.com%2fquestions%2f210315%2fnatural-merge-mergesort-that-uses-already-sorted-subarrays%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Add docstrings and typed arguments. Otherwise it's not bad
– Reinderien
43 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
35 mins ago