recursion doesnt return expected result in python [duplicate]
This question already has an answer here:
Recursion function not working properly
4 answers
Python recursive function doesn't return
3 answers
I try to implement the Longest Common Subsequence problem that it can be found in various online programming challenges. the piece of code is
sub=""
def lcs(x, y):
sub2=sub1=''
global sub
if len(x) == 0 or len(y) == 0:
return sub
if len(x) != 0 and len(y) != 0:
sub1 = [i for i in x][-1]
sub2 = [i for i in y][-1]
if sub1!=sub2:
if len(x) > len(y):
x=x[:-1]
elif len(x) < len(y):
y=y[:-1]
else:
x=x[:-1]
y=y[:-1]
else:
sub=sub+sub1
x=x[:-1]
y=y[:-1]
lcs(x, y)
print lcs('a','a')
i expect the print statement to return 'a' but instead returns None. I think the problem is that the steps of the recursion saves the previous output and when the print is called it reaches these previous results. what am i doing wrong and how should i handle such cases?
python recursion
asked Nov 22 '18 at 16:59
b10n1kb10n1k
316314
marked as duplicate by dani herrera, g.d.d.c, juanpa.arrivillaga python
Users with the python badge can single-handedly close python questions as duplicates and reopen them as needed.
StackExchange.ready(function() {
if (StackExchange.options.isMobile) return;
$('.dupe-hammer-message-hover:not(.hover-bound)').each(function() {
var $hover = $(this).addClass('hover-bound'),
$msg = $hover.siblings('.dupe-hammer-message');
$hover.hover(
function() {
$hover.showInfoMessage('', {
messageElement: $msg.clone().show(),
transient: false,
position: { my: 'bottom left', at: 'top center', offsetTop: -7 },
dismissable: false,
relativeToBody: true
});
},
function() {
StackExchange.helpers.removeMessages();
}
);
});
});
Nov 22 '18 at 17:06
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
add a comment |
This question already has an answer here:
Recursion function not working properly
4 answers
Python recursive function doesn't return
3 answers
I try to implement the Longest Common Subsequence problem that it can be found in various online programming challenges. the piece of code is
sub=""
def lcs(x, y):
sub2=sub1=''
global sub
if len(x) == 0 or len(y) == 0:
return sub
if len(x) != 0 and len(y) != 0:
sub1 = [i for i in x][-1]
sub2 = [i for i in y][-1]
if sub1!=sub2:
if len(x) > len(y):
x=x[:-1]
elif len(x) < len(y):
y=y[:-1]
else:
x=x[:-1]
y=y[:-1]
else:
sub=sub+sub1
x=x[:-1]
y=y[:-1]
lcs(x, y)
print lcs('a','a')
i expect the print statement to return 'a' but instead returns None. I think the problem is that the steps of the recursion saves the previous output and when the print is called it reaches these previous results. what am i doing wrong and how should i handle such cases?
python recursion
asked Nov 22 '18 at 16:59
b10n1kb10n1k
316314
marked as duplicate by dani herrera, g.d.d.c, juanpa.arrivillaga python
Users with the python badge can single-handedly close python questions as duplicates and reopen them as needed.
StackExchange.ready(function() {
if (StackExchange.options.isMobile) return;
$('.dupe-hammer-message-hover:not(.hover-bound)').each(function() {
var $hover = $(this).addClass('hover-bound'),
$msg = $hover.siblings('.dupe-hammer-message');
$hover.hover(
function() {
$hover.showInfoMessage('', {
messageElement: $msg.clone().show(),
transient: false,
position: { my: 'bottom left', at: 'top center', offsetTop: -7 },
dismissable: false,
relativeToBody: true
});
},
function() {
StackExchange.helpers.removeMessages();
}
);
});
});
Nov 22 '18 at 17:06
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
4
You have to return the result of the recursive call.return lcs(x, y).
– g.d.d.c
Nov 22 '18 at 17:03
Note, the second duplicate target was literally the first result I got when I copy-and-pasted your title into a google search. Please try to at least try to find if someone has asked a similar question before you post a new one. I understand sometimes its difficult to articulate if you don't know what is wrong, but again, just googling your title brought me to one...
– juanpa.arrivillaga
Nov 22 '18 at 17:07
add a comment |
This question already has an answer here:
Recursion function not working properly
4 answers
Python recursive function doesn't return
3 answers
I try to implement the Longest Common Subsequence problem that it can be found in various online programming challenges. the piece of code is
sub=""
def lcs(x, y):
sub2=sub1=''
global sub
if len(x) == 0 or len(y) == 0:
return sub
if len(x) != 0 and len(y) != 0:
sub1 = [i for i in x][-1]
sub2 = [i for i in y][-1]
if sub1!=sub2:
if len(x) > len(y):
x=x[:-1]
elif len(x) < len(y):
y=y[:-1]
else:
x=x[:-1]
y=y[:-1]
else:
sub=sub+sub1
x=x[:-1]
y=y[:-1]
lcs(x, y)
print lcs('a','a')
i expect the print statement to return 'a' but instead returns None. I think the problem is that the steps of the recursion saves the previous output and when the print is called it reaches these previous results. what am i doing wrong and how should i handle such cases?
python recursion
asked Nov 22 '18 at 16:59
b10n1kb10n1k
316314
This question already has an answer here:
Recursion function not working properly
4 answers
Python recursive function doesn't return
3 answers
I try to implement the Longest Common Subsequence problem that it can be found in various online programming challenges. the piece of code is
sub=""
def lcs(x, y):
sub2=sub1=''
global sub
if len(x) == 0 or len(y) == 0:
return sub
if len(x) != 0 and len(y) != 0:
sub1 = [i for i in x][-1]
sub2 = [i for i in y][-1]
if sub1!=sub2:
if len(x) > len(y):
x=x[:-1]
elif len(x) < len(y):
y=y[:-1]
else:
x=x[:-1]
y=y[:-1]
else:
sub=sub+sub1
x=x[:-1]
y=y[:-1]
lcs(x, y)
print lcs('a','a')
i expect the print statement to return 'a' but instead returns None. I think the problem is that the steps of the recursion saves the previous output and when the print is called it reaches these previous results. what am i doing wrong and how should i handle such cases?
This question already has an answer here:
Recursion function not working properly
4 answers
Python recursive function doesn't return
3 answers
python recursion
python recursion
asked Nov 22 '18 at 16:59
b10n1kb10n1k
316314
asked Nov 22 '18 at 16:59
b10n1kb10n1k
316314
asked Nov 22 '18 at 16:59
b10n1kb10n1k
316314
asked Nov 22 '18 at 16:59
b10n1kb10n1k
316314
asked Nov 22 '18 at 16:59
b10n1kb10n1k
316314
316314
marked as duplicate by dani herrera, g.d.d.c, juanpa.arrivillaga python
Users with the python badge can single-handedly close python questions as duplicates and reopen them as needed.
StackExchange.ready(function() {
if (StackExchange.options.isMobile) return;
$('.dupe-hammer-message-hover:not(.hover-bound)').each(function() {
var $hover = $(this).addClass('hover-bound'),
$msg = $hover.siblings('.dupe-hammer-message');
$hover.hover(
function() {
$hover.showInfoMessage('', {
messageElement: $msg.clone().show(),
transient: false,
position: { my: 'bottom left', at: 'top center', offsetTop: -7 },
dismissable: false,
relativeToBody: true
});
},
function() {
StackExchange.helpers.removeMessages();
}
);
});
});
Nov 22 '18 at 17:06
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
marked as duplicate by dani herrera, g.d.d.c, juanpa.arrivillaga python
Users with the python badge can single-handedly close python questions as duplicates and reopen them as needed.
StackExchange.ready(function() {
if (StackExchange.options.isMobile) return;
$('.dupe-hammer-message-hover:not(.hover-bound)').each(function() {
var $hover = $(this).addClass('hover-bound'),
$msg = $hover.siblings('.dupe-hammer-message');
$hover.hover(
function() {
$hover.showInfoMessage('', {
messageElement: $msg.clone().show(),
transient: false,
position: { my: 'bottom left', at: 'top center', offsetTop: -7 },
dismissable: false,
relativeToBody: true
});
},
function() {
StackExchange.helpers.removeMessages();
}
);
});
});
Nov 22 '18 at 17:06
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
4
You have to return the result of the recursive call.return lcs(x, y).
– g.d.d.c
Nov 22 '18 at 17:03
Note, the second duplicate target was literally the first result I got when I copy-and-pasted your title into a google search. Please try to at least try to find if someone has asked a similar question before you post a new one. I understand sometimes its difficult to articulate if you don't know what is wrong, but again, just googling your title brought me to one...
– juanpa.arrivillaga
Nov 22 '18 at 17:07
add a comment |
4
You have to return the result of the recursive call.return lcs(x, y).
– g.d.d.c
Nov 22 '18 at 17:03
Note, the second duplicate target was literally the first result I got when I copy-and-pasted your title into a google search. Please try to at least try to find if someone has asked a similar question before you post a new one. I understand sometimes its difficult to articulate if you don't know what is wrong, but again, just googling your title brought me to one...
– juanpa.arrivillaga
Nov 22 '18 at 17:07
4
4
You have to return the result of the recursive call.
return lcs(x, y).– g.d.d.c
Nov 22 '18 at 17:03
You have to return the result of the recursive call.
return lcs(x, y).– g.d.d.c
Nov 22 '18 at 17:03
Note, the second duplicate target was literally the first result I got when I copy-and-pasted your title into a google search. Please try to at least try to find if someone has asked a similar question before you post a new one. I understand sometimes its difficult to articulate if you don't know what is wrong, but again, just googling your title brought me to one...
– juanpa.arrivillaga
Nov 22 '18 at 17:07
Note, the second duplicate target was literally the first result I got when I copy-and-pasted your title into a google search. Please try to at least try to find if someone has asked a similar question before you post a new one. I understand sometimes its difficult to articulate if you don't know what is wrong, but again, just googling your title brought me to one...
– juanpa.arrivillaga
Nov 22 '18 at 17:07
add a comment |
0
active
oldest
votes
0
active
oldest
votes
0
active
oldest
votes
active
oldest
votes
active
oldest
votes
4
You have to return the result of the recursive call.
return lcs(x, y).– g.d.d.c
Nov 22 '18 at 17:03
Note, the second duplicate target was literally the first result I got when I copy-and-pasted your title into a google search. Please try to at least try to find if someone has asked a similar question before you post a new one. I understand sometimes its difficult to articulate if you don't know what is wrong, but again, just googling your title brought me to one...
– juanpa.arrivillaga
Nov 22 '18 at 17:07