C++: Insert vector into anonymous vector, recursively
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My goal is to generate vector with pattern {1} given max_=2, {1,2,1} given max_=3, {1,2,1,3,1,2,1} given max_=4... etc
Here is my psuedocode:
std::vector<int> generate_zimin(int max_)
{
if(max_ == 2)
{
return {1};
}
else
{
return {generate_zimin(max_-1), (max_-1), generate_zimin(max_-1)};
}
}
How do I insert vectors into an anonymous vector?
edit:
std::vector<int> generate_zimin(std::vector<int> current, int max_)
{
if(max_ == 2)
{
return {1};
}
else
{
std::vector<int> prev = generate_zimin(current, max_-1);
current.insert(current.end(), std::begin(prev), std::end(prev));
current.push_back(max_-1);
current.insert(current.end(), std::begin(prev), std::end(prev));
return current;
}
}
looks a lot less elegant, and I was just trying to avoid that, but I can see
why I was wrong.
c++ recursion vector
asked Nov 24 '18 at 3:54
Bo WorkBo Work
104
add a comment |
My goal is to generate vector with pattern {1} given max_=2, {1,2,1} given max_=3, {1,2,1,3,1,2,1} given max_=4... etc
Here is my psuedocode:
std::vector<int> generate_zimin(int max_)
{
if(max_ == 2)
{
return {1};
}
else
{
return {generate_zimin(max_-1), (max_-1), generate_zimin(max_-1)};
}
}
How do I insert vectors into an anonymous vector?
edit:
std::vector<int> generate_zimin(std::vector<int> current, int max_)
{
if(max_ == 2)
{
return {1};
}
else
{
std::vector<int> prev = generate_zimin(current, max_-1);
current.insert(current.end(), std::begin(prev), std::end(prev));
current.push_back(max_-1);
current.insert(current.end(), std::begin(prev), std::end(prev));
return current;
}
}
looks a lot less elegant, and I was just trying to avoid that, but I can see
why I was wrong.
c++ recursion vector
asked Nov 24 '18 at 3:54
Bo WorkBo Work
104
You don't. Why does it have to be "anonymous"? What's wrong with using a local variable to accumulate the result?
– Igor Tandetnik
Nov 24 '18 at 3:56
There isn't really a way to do it in a one-liner. See this question about concatenating vectors: stackoverflow.com/questions/201718/concatenating-two-stdvectors
– alter igel
Nov 24 '18 at 3:56
@IgorTandetnik By using local variable, I should declare an empty vector at the start of the function, and append generate_zimin(max_-1) to it, then push_back max_-1 to it, then append generate_zimin(max_z-1), then return it?
– Bo Work
Nov 24 '18 at 4:14
add a comment |
My goal is to generate vector with pattern {1} given max_=2, {1,2,1} given max_=3, {1,2,1,3,1,2,1} given max_=4... etc
Here is my psuedocode:
std::vector<int> generate_zimin(int max_)
{
if(max_ == 2)
{
return {1};
}
else
{
return {generate_zimin(max_-1), (max_-1), generate_zimin(max_-1)};
}
}
How do I insert vectors into an anonymous vector?
edit:
std::vector<int> generate_zimin(std::vector<int> current, int max_)
{
if(max_ == 2)
{
return {1};
}
else
{
std::vector<int> prev = generate_zimin(current, max_-1);
current.insert(current.end(), std::begin(prev), std::end(prev));
current.push_back(max_-1);
current.insert(current.end(), std::begin(prev), std::end(prev));
return current;
}
}
looks a lot less elegant, and I was just trying to avoid that, but I can see
why I was wrong.
c++ recursion vector
asked Nov 24 '18 at 3:54
Bo WorkBo Work
104
My goal is to generate vector with pattern {1} given max_=2, {1,2,1} given max_=3, {1,2,1,3,1,2,1} given max_=4... etc
Here is my psuedocode:
std::vector<int> generate_zimin(int max_)
{
if(max_ == 2)
{
return {1};
}
else
{
return {generate_zimin(max_-1), (max_-1), generate_zimin(max_-1)};
}
}
How do I insert vectors into an anonymous vector?
edit:
std::vector<int> generate_zimin(std::vector<int> current, int max_)
{
if(max_ == 2)
{
return {1};
}
else
{
std::vector<int> prev = generate_zimin(current, max_-1);
current.insert(current.end(), std::begin(prev), std::end(prev));
current.push_back(max_-1);
current.insert(current.end(), std::begin(prev), std::end(prev));
return current;
}
}
looks a lot less elegant, and I was just trying to avoid that, but I can see
why I was wrong.
c++ recursion vector
c++ recursion vector
asked Nov 24 '18 at 3:54
Bo WorkBo Work
104
asked Nov 24 '18 at 3:54
Bo WorkBo Work
104
edited Nov 24 '18 at 4:48
Bo Work
asked Nov 24 '18 at 3:54
Bo WorkBo Work
104
asked Nov 24 '18 at 3:54
Bo WorkBo Work
104
asked Nov 24 '18 at 3:54
Bo WorkBo Work
104
104
You don't. Why does it have to be "anonymous"? What's wrong with using a local variable to accumulate the result?
– Igor Tandetnik
Nov 24 '18 at 3:56
There isn't really a way to do it in a one-liner. See this question about concatenating vectors: stackoverflow.com/questions/201718/concatenating-two-stdvectors
– alter igel
Nov 24 '18 at 3:56
@IgorTandetnik By using local variable, I should declare an empty vector at the start of the function, and append generate_zimin(max_-1) to it, then push_back max_-1 to it, then append generate_zimin(max_z-1), then return it?
– Bo Work
Nov 24 '18 at 4:14
add a comment |
You don't. Why does it have to be "anonymous"? What's wrong with using a local variable to accumulate the result?
– Igor Tandetnik
Nov 24 '18 at 3:56
There isn't really a way to do it in a one-liner. See this question about concatenating vectors: stackoverflow.com/questions/201718/concatenating-two-stdvectors
– alter igel
Nov 24 '18 at 3:56
@IgorTandetnik By using local variable, I should declare an empty vector at the start of the function, and append generate_zimin(max_-1) to it, then push_back max_-1 to it, then append generate_zimin(max_z-1), then return it?
– Bo Work
Nov 24 '18 at 4:14
You don't. Why does it have to be "anonymous"? What's wrong with using a local variable to accumulate the result?
– Igor Tandetnik
Nov 24 '18 at 3:56
You don't. Why does it have to be "anonymous"? What's wrong with using a local variable to accumulate the result?
– Igor Tandetnik
Nov 24 '18 at 3:56
There isn't really a way to do it in a one-liner. See this question about concatenating vectors: stackoverflow.com/questions/201718/concatenating-two-stdvectors
– alter igel
Nov 24 '18 at 3:56
There isn't really a way to do it in a one-liner. See this question about concatenating vectors: stackoverflow.com/questions/201718/concatenating-two-stdvectors
– alter igel
Nov 24 '18 at 3:56
@IgorTandetnik By using local variable, I should declare an empty vector at the start of the function, and append generate_zimin(max_-1) to it, then push_back max_-1 to it, then append generate_zimin(max_z-1), then return it?
– Bo Work
Nov 24 '18 at 4:14
@IgorTandetnik By using local variable, I should declare an empty vector at the start of the function, and append generate_zimin(max_-1) to it, then push_back max_-1 to it, then append generate_zimin(max_z-1), then return it?
– Bo Work
Nov 24 '18 at 4:14
add a comment |
1 Answer
1
active
oldest
votes
Not only is there no syntax for this, it is a bad idea for performance. You'll be allocating and deallocating vectors on every function call. You should create a single vector at the beginning and use it in all the calls. This could improve performance by a factor of 100.
You can even calculate the total size of the vector at the beginning and reserve() the needed capacity.
answered Nov 24 '18 at 3:58
John ZwinckJohn Zwinck
155k17181300
How would I reserve the needed capacity when its function is also recursive? A generate_zimin(n)'s total space = 2*generate_zimin(n-1)'s total space +1. I must be overthinking this too much
– Bo Work
Nov 24 '18 at 4:10
Total capacities are 1, 3, 7, 15, 31. Punch that into a search and voila: oeis.org/A000225 - it is2^n - 1.
– John Zwinck
Nov 24 '18 at 4:24
add a comment |
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1 Answer
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1 Answer
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oldest
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oldest
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oldest
votes
Not only is there no syntax for this, it is a bad idea for performance. You'll be allocating and deallocating vectors on every function call. You should create a single vector at the beginning and use it in all the calls. This could improve performance by a factor of 100.
You can even calculate the total size of the vector at the beginning and reserve() the needed capacity.
answered Nov 24 '18 at 3:58
John ZwinckJohn Zwinck
155k17181300
How would I reserve the needed capacity when its function is also recursive? A generate_zimin(n)'s total space = 2*generate_zimin(n-1)'s total space +1. I must be overthinking this too much
– Bo Work
Nov 24 '18 at 4:10
Total capacities are 1, 3, 7, 15, 31. Punch that into a search and voila: oeis.org/A000225 - it is2^n - 1.
– John Zwinck
Nov 24 '18 at 4:24
add a comment |
Not only is there no syntax for this, it is a bad idea for performance. You'll be allocating and deallocating vectors on every function call. You should create a single vector at the beginning and use it in all the calls. This could improve performance by a factor of 100.
You can even calculate the total size of the vector at the beginning and reserve() the needed capacity.
answered Nov 24 '18 at 3:58
John ZwinckJohn Zwinck
155k17181300
How would I reserve the needed capacity when its function is also recursive? A generate_zimin(n)'s total space = 2*generate_zimin(n-1)'s total space +1. I must be overthinking this too much
– Bo Work
Nov 24 '18 at 4:10
Total capacities are 1, 3, 7, 15, 31. Punch that into a search and voila: oeis.org/A000225 - it is2^n - 1.
– John Zwinck
Nov 24 '18 at 4:24
add a comment |
Not only is there no syntax for this, it is a bad idea for performance. You'll be allocating and deallocating vectors on every function call. You should create a single vector at the beginning and use it in all the calls. This could improve performance by a factor of 100.
You can even calculate the total size of the vector at the beginning and reserve() the needed capacity.
answered Nov 24 '18 at 3:58
John ZwinckJohn Zwinck
155k17181300
Not only is there no syntax for this, it is a bad idea for performance. You'll be allocating and deallocating vectors on every function call. You should create a single vector at the beginning and use it in all the calls. This could improve performance by a factor of 100.
You can even calculate the total size of the vector at the beginning and reserve() the needed capacity.
answered Nov 24 '18 at 3:58
John ZwinckJohn Zwinck
155k17181300
answered Nov 24 '18 at 3:58
John ZwinckJohn Zwinck
155k17181300
answered Nov 24 '18 at 3:58
John ZwinckJohn Zwinck
155k17181300
answered Nov 24 '18 at 3:58
John ZwinckJohn Zwinck
155k17181300
155k17181300
How would I reserve the needed capacity when its function is also recursive? A generate_zimin(n)'s total space = 2*generate_zimin(n-1)'s total space +1. I must be overthinking this too much
– Bo Work
Nov 24 '18 at 4:10
Total capacities are 1, 3, 7, 15, 31. Punch that into a search and voila: oeis.org/A000225 - it is2^n - 1.
– John Zwinck
Nov 24 '18 at 4:24
add a comment |
How would I reserve the needed capacity when its function is also recursive? A generate_zimin(n)'s total space = 2*generate_zimin(n-1)'s total space +1. I must be overthinking this too much
– Bo Work
Nov 24 '18 at 4:10
Total capacities are 1, 3, 7, 15, 31. Punch that into a search and voila: oeis.org/A000225 - it is2^n - 1.
– John Zwinck
Nov 24 '18 at 4:24
How would I reserve the needed capacity when its function is also recursive? A generate_zimin(n)'s total space = 2*generate_zimin(n-1)'s total space +1. I must be overthinking this too much
– Bo Work
Nov 24 '18 at 4:10
How would I reserve the needed capacity when its function is also recursive? A generate_zimin(n)'s total space = 2*generate_zimin(n-1)'s total space +1. I must be overthinking this too much
– Bo Work
Nov 24 '18 at 4:10
Total capacities are 1, 3, 7, 15, 31. Punch that into a search and voila: oeis.org/A000225 - it is
2^n - 1.– John Zwinck
Nov 24 '18 at 4:24
Total capacities are 1, 3, 7, 15, 31. Punch that into a search and voila: oeis.org/A000225 - it is
2^n - 1.– John Zwinck
Nov 24 '18 at 4:24
add a comment |
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You don't. Why does it have to be "anonymous"? What's wrong with using a local variable to accumulate the result?
– Igor Tandetnik
Nov 24 '18 at 3:56
There isn't really a way to do it in a one-liner. See this question about concatenating vectors: stackoverflow.com/questions/201718/concatenating-two-stdvectors
– alter igel
Nov 24 '18 at 3:56
@IgorTandetnik By using local variable, I should declare an empty vector at the start of the function, and append generate_zimin(max_-1) to it, then push_back max_-1 to it, then append generate_zimin(max_z-1), then return it?
– Bo Work
Nov 24 '18 at 4:14