Embarrassing code admission of the day (or why C.S. is good for you)
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Pretend the overall logic is entirely sound. The bug below is very subtle and is not a logic bug but a design bug, to make it harder, pretend the overall logic is correct. What is the bug?
//init the list and fill it
List fakeList = new List();
//Find the subtle bug
while (fakeList.Count > 0) {
double temp = fakeList[0];
//..do something
fakeList.RemoveAt(0);
}Hint: Ok, if it is too hard. Remember what a List is in C# and then remember the specifics of that data structure from intro to programming. Edit: The data structure is correct, and the logic is technically correct but wrong. Another Hint: Run it with a populated list of 100,000 elements and check the timing. There is a particular feature of this data structure that happens with this particular code that one small change would avoid.
Need custom software developed? I do custom programming based primarily on MS tools with an emphasis on C# development and consulting. I also do Android Programming as I find it a refreshing break from the MS. "And they, since they Were not the one dead, turned to their affairs" -- Robert Frost
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No, it's not a
foreach.If you truly believe you need to pick a mobile phone that "says something" about your personality, don't bother. You don't have a personality. A mental illness, maybe, but not a personality. [Charlie Brooker] ScrewTurn Wiki, Software Localization Tools & Services and My Blog
Quite right!
Sort of a cross between Lawrence of Arabia and Dilbert.[^]
-Or-
A Dead ringer for Kate Winslett[^] -
Pretend the overall logic is entirely sound. The bug below is very subtle and is not a logic bug but a design bug, to make it harder, pretend the overall logic is correct. What is the bug?
//init the list and fill it
List fakeList = new List();
//Find the subtle bug
while (fakeList.Count > 0) {
double temp = fakeList[0];
//..do something
fakeList.RemoveAt(0);
}Hint: Ok, if it is too hard. Remember what a List is in C# and then remember the specifics of that data structure from intro to programming. Edit: The data structure is correct, and the logic is technically correct but wrong. Another Hint: Run it with a populated list of 100,000 elements and check the timing. There is a particular feature of this data structure that happens with this particular code that one small change would avoid.
Need custom software developed? I do custom programming based primarily on MS tools with an emphasis on C# development and consulting. I also do Android Programming as I find it a refreshing break from the MS. "And they, since they Were not the one dead, turned to their affairs" -- Robert Frost
fakeList[0] fakeList[0] fakeList[0] fakeList[0] Indexer on a list? [edit] For those who are asking - I'm suggesting that it might be a problem since accessing Nth element in the list has O(n) complexity.
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fakeList[0] fakeList[0] fakeList[0] fakeList[0] Indexer on a list? [edit] For those who are asking - I'm suggesting that it might be a problem since accessing Nth element in the list has O(n) complexity.
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fakeList[0] fakeList[0] fakeList[0] fakeList[0] Indexer on a list? [edit] For those who are asking - I'm suggesting that it might be a problem since accessing Nth element in the list has O(n) complexity.
It's allowed. How else would you get the value at position
i?*pre-emptive celebratory nipple tassle jiggle* - Sean Ewington
"Mind bleach! Send me mind bleach!" - Nagy Vilmos
My blog | My articles | MoXAML PowerToys | Mole 2010 - debugging made easier - my favourite utility
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Pretend the overall logic is entirely sound. The bug below is very subtle and is not a logic bug but a design bug, to make it harder, pretend the overall logic is correct. What is the bug?
//init the list and fill it
List fakeList = new List();
//Find the subtle bug
while (fakeList.Count > 0) {
double temp = fakeList[0];
//..do something
fakeList.RemoveAt(0);
}Hint: Ok, if it is too hard. Remember what a List is in C# and then remember the specifics of that data structure from intro to programming. Edit: The data structure is correct, and the logic is technically correct but wrong. Another Hint: Run it with a populated list of 100,000 elements and check the timing. There is a particular feature of this data structure that happens with this particular code that one small change would avoid.
Need custom software developed? I do custom programming based primarily on MS tools with an emphasis on C# development and consulting. I also do Android Programming as I find it a refreshing break from the MS. "And they, since they Were not the one dead, turned to their affairs" -- Robert Frost
Cannot find any bug.
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O(n)?
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Pretend the overall logic is entirely sound. The bug below is very subtle and is not a logic bug but a design bug, to make it harder, pretend the overall logic is correct. What is the bug?
//init the list and fill it
List fakeList = new List();
//Find the subtle bug
while (fakeList.Count > 0) {
double temp = fakeList[0];
//..do something
fakeList.RemoveAt(0);
}Hint: Ok, if it is too hard. Remember what a List is in C# and then remember the specifics of that data structure from intro to programming. Edit: The data structure is correct, and the logic is technically correct but wrong. Another Hint: Run it with a populated list of 100,000 elements and check the timing. There is a particular feature of this data structure that happens with this particular code that one small change would avoid.
Need custom software developed? I do custom programming based primarily on MS tools with an emphasis on C# development and consulting. I also do Android Programming as I find it a refreshing break from the MS. "And they, since they Were not the one dead, turned to their affairs" -- Robert Frost
Took me a moment or two to spot that. Couldn't really see it until I thought it through. Good catch - how did you find it? For others - what happens when you remove at 0? How is this handled in terms of resizing when you remove from the start of the list. As a comparison, remove from the last position instead (ok, it's not the same logical code, but it shows timings).
*pre-emptive celebratory nipple tassle jiggle* - Sean Ewington
"Mind bleach! Send me mind bleach!" - Nagy Vilmos
My blog | My articles | MoXAML PowerToys | Mole 2010 - debugging made easier - my favourite utility
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fakeList[0] fakeList[0] fakeList[0] fakeList[0] Indexer on a list? [edit] For those who are asking - I'm suggesting that it might be a problem since accessing Nth element in the list has O(n) complexity.
yes. list being the simplest data type in which an order is applied to a set of data Though, judging by your rep scores on here you are more likely to know what you are talking about than I am, so ... am i missing something here, do we work in different languages with different concepts of 'list'? should we be using
list.ElementAt(0)
instead?
Pedis ex oris Quidquid latine dictum sit, altum sonatur
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It's allowed. How else would you get the value at position
i?*pre-emptive celebratory nipple tassle jiggle* - Sean Ewington
"Mind bleach! Send me mind bleach!" - Nagy Vilmos
My blog | My articles | MoXAML PowerToys | Mole 2010 - debugging made easier - my favourite utility
Yes it is, But also it has O(n) complexity.
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Cannot find any bug.
It's not a bug per se, it's an efficiency thing.
*pre-emptive celebratory nipple tassle jiggle* - Sean Ewington
"Mind bleach! Send me mind bleach!" - Nagy Vilmos
My blog | My articles | MoXAML PowerToys | Mole 2010 - debugging made easier - my favourite utility
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Pretend the overall logic is entirely sound. The bug below is very subtle and is not a logic bug but a design bug, to make it harder, pretend the overall logic is correct. What is the bug?
//init the list and fill it
List fakeList = new List();
//Find the subtle bug
while (fakeList.Count > 0) {
double temp = fakeList[0];
//..do something
fakeList.RemoveAt(0);
}Hint: Ok, if it is too hard. Remember what a List is in C# and then remember the specifics of that data structure from intro to programming. Edit: The data structure is correct, and the logic is technically correct but wrong. Another Hint: Run it with a populated list of 100,000 elements and check the timing. There is a particular feature of this data structure that happens with this particular code that one small change would avoid.
Need custom software developed? I do custom programming based primarily on MS tools with an emphasis on C# development and consulting. I also do Android Programming as I find it a refreshing break from the MS. "And they, since they Were not the one dead, turned to their affairs" -- Robert Frost
Ennis Ray Lynch, Jr. wrote:
Another Hint: Run it with a populated list of 100,000 elements and check the timing. There is a particular feature of this data structure that happens with this particular code that one small change would avoid.
But that is not called a bug, is it?
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fakeList[0] fakeList[0] fakeList[0] fakeList[0] Indexer on a list? [edit] For those who are asking - I'm suggesting that it might be a problem since accessing Nth element in the list has O(n) complexity.
Didn't think that deserved a 1. Corrected. As a hint, the answer has to do with which side of the list you remove the element from. How is it handled re, resizing?
*pre-emptive celebratory nipple tassle jiggle* - Sean Ewington
"Mind bleach! Send me mind bleach!" - Nagy Vilmos
My blog | My articles | MoXAML PowerToys | Mole 2010 - debugging made easier - my favourite utility
-
Pretend the overall logic is entirely sound. The bug below is very subtle and is not a logic bug but a design bug, to make it harder, pretend the overall logic is correct. What is the bug?
//init the list and fill it
List fakeList = new List();
//Find the subtle bug
while (fakeList.Count > 0) {
double temp = fakeList[0];
//..do something
fakeList.RemoveAt(0);
}Hint: Ok, if it is too hard. Remember what a List is in C# and then remember the specifics of that data structure from intro to programming. Edit: The data structure is correct, and the logic is technically correct but wrong. Another Hint: Run it with a populated list of 100,000 elements and check the timing. There is a particular feature of this data structure that happens with this particular code that one small change would avoid.
Need custom software developed? I do custom programming based primarily on MS tools with an emphasis on C# development and consulting. I also do Android Programming as I find it a refreshing break from the MS. "And they, since they Were not the one dead, turned to their affairs" -- Robert Frost
Ah. Now you see, that is another example as to why programming is hard.
Sort of a cross between Lawrence of Arabia and Dilbert.[^]
-Or-
A Dead ringer for Kate Winslett[^] -
O(n)?
-
Pretend the overall logic is entirely sound. The bug below is very subtle and is not a logic bug but a design bug, to make it harder, pretend the overall logic is correct. What is the bug?
//init the list and fill it
List fakeList = new List();
//Find the subtle bug
while (fakeList.Count > 0) {
double temp = fakeList[0];
//..do something
fakeList.RemoveAt(0);
}Hint: Ok, if it is too hard. Remember what a List is in C# and then remember the specifics of that data structure from intro to programming. Edit: The data structure is correct, and the logic is technically correct but wrong. Another Hint: Run it with a populated list of 100,000 elements and check the timing. There is a particular feature of this data structure that happens with this particular code that one small change would avoid.
Need custom software developed? I do custom programming based primarily on MS tools with an emphasis on C# development and consulting. I also do Android Programming as I find it a refreshing break from the MS. "And they, since they Were not the one dead, turned to their affairs" -- Robert Frost
Not sure if it's intended or not but you're going to delete the list by deleting the first item over and over?
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Took me a moment or two to spot that. Couldn't really see it until I thought it through. Good catch - how did you find it? For others - what happens when you remove at 0? How is this handled in terms of resizing when you remove from the start of the list. As a comparison, remove from the last position instead (ok, it's not the same logical code, but it shows timings).
*pre-emptive celebratory nipple tassle jiggle* - Sean Ewington
"Mind bleach! Send me mind bleach!" - Nagy Vilmos
My blog | My articles | MoXAML PowerToys | Mole 2010 - debugging made easier - my favourite utility
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Yes it is, But also it has O(n) complexity.
When n = 0, you could have an exponential cost, it wouldn't matter much, now would it?
'As programmers go, I'm fairly social. Which still means I'm a borderline sociopath by normal standards.' Jeff Atwood 'I'm French! Why do you think I've got this outrrrrageous accent?' Monty Python and the Holy Grail
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Ennis Ray Lynch, Jr. wrote:
Another Hint: Run it with a populated list of 100,000 elements and check the timing. There is a particular feature of this data structure that happens with this particular code that one small change would avoid.
But that is not called a bug, is it?
Yes it is! http://www.codinghorror.com/blog/2011/06/performance-is-a-feature.html[^]
'As programmers go, I'm fairly social. Which still means I'm a borderline sociopath by normal standards.' Jeff Atwood 'I'm French! Why do you think I've got this outrrrrageous accent?' Monty Python and the Holy Grail
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Not sure if it's intended or not but you're going to delete the list by deleting the first item over and over?
Basically, one way or the other there's a 0(n) operation - either in finding the element at position n, or removing the element at position n. Removing the element at n where n = 0 would, at first glance, appear to be a good optimisation. Unfortunately, it has side effects.
*pre-emptive celebratory nipple tassle jiggle* - Sean Ewington
"Mind bleach! Send me mind bleach!" - Nagy Vilmos
My blog | My articles | MoXAML PowerToys | Mole 2010 - debugging made easier - my favourite utility
