Closed. This question needs details or clarity. It is not currently accepting answers.
Want to improve this question? Add details and clarify the problem by editing this post.
Closed 8 years ago.
Improve this question
So to cut a long story short, I am trying to implement countsort for vector. I have some error somewhere in my code, though I think that I have followed the pseudo code pretty strictly.
The function:
void csort(vector<int>& a, vector<int>& b)
{
vector<int> c(a.size());
for(int i = 0; i <= c.size(); i++)
c[i] = 0;
for(int i = 0; i <= a.size(); i++ )
{
c[a[i]]++;
}
for(int i = 0; i <= c.size(); i++)
{
c[i]+= c[i-1];
}
for(int i = a.size(); i < 1; i--)
{
b[c[a[i]]] = a[i];
c[a[i]] =c[a[i]] -1;
}
}
The pesudo code:
let C[k] be a new array
for i = 0 to k
C[i] = 0
for j = 1 to A:length
C[A[j]] = C[A[j]] +1
for i = 1 to k
C[i] = C[i]+ C[i-1]
for j = A:length downto 1
B[C[A[j]]] = A[j]
C[A[j]] = C[A[j]] -1
The code as it is is very unreadable and error prone. In any case, what I first saw is that in the snippet below you will access c[-1] at the first iteration, thus incurring in undefined behaviour.
for (int i = 0; i <= c.size(); i++)
{
c[i] += c[i-1]; // Evaluation of c[i-1] is illegal for i == 0
}
for(int i = a.size(); i < 1; i--)
This code won't work at all.
for j = A:length downto 1
↑
To implement this pseudo code, you should do like this
for(int i(a.size()-1);i>=0;--i)
And for code like this( c[a[i]] )，you will get run-time error if a[i]<0 or a[i]>=c.size()
Related
Closed. This question needs debugging details. It is not currently accepting answers.
Edit the question to include desired behavior, a specific problem or error, and the shortest code necessary to reproduce the problem. This will help others answer the question.
Closed 2 years ago.
Improve this question
So I need help. The problem is that an int arr[5] = {0};
I know the array has the values {0,0,0,0,0} filling the whole array. At the end of the code the array must have the values {1,2,3,4,5} inside it. To solve it must use a nested for loop.
I have tried the following code
Sorry if there is an error in the way this question is formatted this is my first time and using mobile.
int arr[5] = {0};
for(int j = 1; j<6; j++)
{
for(int i = 0; i<5; i++)
{
arr[i] = j;
}
}
I don't know what the benefit of that but If you have to use nested for loop, the following is an option
int main()
{
int arr[5] = {0};
for(int j = 0; j < 5; ++j)
{
for(int i = 1; i < 2; ++i)
{
arr[j] = j+i;
}
}
for(int i{};i<5;++i) std::cout << arr[i] << ", ";
}
Or like #JaMit comment suggests
int main()
{
int arr[5] = {0};
for(int j = 0; j < 5; ++j)
{
for(int i = 0; i < j+1; ++i)
{
arr[j]++;
}
}
for(int i{};i<5;++i) std::cout << arr[i] << ", ";
}
I'm guessing your professor means you should generate the final results using only incrementation. In other words, I'm guessing you're not allowed to assign values after the int arr[5] = {0}; line (so an expression like arr[i] = j; is not allowed).
In that case, you could solve the problem as follows:
int arr[5] = {0};
for (int i = 0; i < 5; i++) {
for (int j = i; j < 5; j++) {
arr[j]++;
}
}
Now we have only used incrementation and the final result is {1, 2, 3, 4, 5}.
Closed. This question needs details or clarity. It is not currently accepting answers.
Want to improve this question? Add details and clarify the problem by editing this post.
Closed 4 years ago.
Improve this question
How to dynamically fill the following output in a two-dimensional array with the same number of rows and columns.
Edit: Here is the solution in c++ using #TheGeneral code from c#.
#include <iostream>
using namespace std;
int main(){
int size = 10;
int half = size/2;
int matrix[size][size];
int number1 = 0;
int number2 = 0;
for(int i = 1; i<=size; i++){
for(int j = 1; j<= size; j++){
if(i > half){
number1 = size + 1 - i;
}else{
number1 = i;
}
if(j > half){
number2 = size + 1 - j;
}else{
number2 = j;
}
if(number1 < number2){
matrix[i-1][j-1] = number1;
}else{
matrix[i-1][j-1] = number2;
}
}
}
cout<<"MATRIX:"<<endl;
for(int i=0; i<size; i++){
for(int j=0; j<size; j++){
cout<<"["<<matrix[i][j]<<"] \t";
}
cout<<endl;
}
return 0;
}
For a bit of fun
The only note worthy things going on, are
Starting the index from 1 (makes things easier)
Conditional Operator to say if an index is greater than 5 reverse the count
Math.Min to make it syemtrical
Exmaple
private static int[, ] CreateArray()
{
var ary = new int[10, 10];
for (var i = 1; i <= 10; i++)
for (var j = 1; j <= 10; j++)
ary[i - 1, j - 1] = Math.Min(i > 5 ? 11 - i : i, j > 5 ? 11 - j : j);
return ary;
}
Demo here
Closed. This question needs debugging details. It is not currently accepting answers.
Edit the question to include desired behavior, a specific problem or error, and the shortest code necessary to reproduce the problem. This will help others answer the question.
Closed 7 years ago.
Improve this question
Here is my C++ code for counting sort algorithm , there is no errors as well as no warnings but when I want to execute it it's give me "Counting.exe has stopped working" I think it is a run time error.
void Counting_sort()
{
int A[]={5,15,20,30,40,8,36,25,96,15,40,15,96,47,20};
int k = 15 ;
int n = 15;
int i, j;
int B[15];
int C[100];
for(i = 0; i <= k; i++)
C[i] = 0;
for(j =1; j <= n; j++)
C[A[j]] = C[A[j]] + 1;
for(i = 1; i <= k; i++)
C[i] = C[i] + C[i-1];
for(j = n; j >= 1; j--)
{
B[C[A[j]]] = A[j];
C[A[j]] = C[A[j]] - 1;
}
cout << "\nThe Sorted array is : ";
for(i = 1; i <= n; i++)
cout << B[i] << " " ;
}
void main()
{
Counting_sort();
}
for(j = n; j >= 1; j--)
{
// You are accessing A[j]
}
So A[15] is a invalid access and will lead to undefined behavior.
The valid access for array A[15] is A[0] to A[14] anything other than this is array out of bound access.
Closed. This question needs details or clarity. It is not currently accepting answers.
Want to improve this question? Add details and clarify the problem by editing this post.
Closed 8 years ago.
Improve this question
I have an array that keeps the number of each element.
int total[5] = {2,3,4,5,6}
int num = 5; //array total has 5 elements
This means that we have 2 element 0's, 3 element 1's in our original array. We are not worried about the original array since I already have a code to keep the number of the elements.
I need a nested for loop that creates a new array that looks like this:
array[0] = 1;
array[1] = 1;
array[2] = 5;
array[3] = 5;
array[4] = 5;
array[5] = 9;
array[6] = 9;
array[7] = 9;
array[8] = 9;
and so on. That is, we store a value in our new array as many as the its value in "total" array. Values 1,5,9, etc. are stored in an array called element. I have something like this so far:
for (int i = 0; i < num; i++){
for (int j = 0; j < total[i]; j++){
array[i + j] = element[i];
}
}
Can somebody help me to figure this out?
An easy solution (though not necessarily elegant) is to do the following:
int count = 0;
for (int i = 0; i < num; i++){
for (int j = 0; j < total[i]; j++){
array[count] = element[i];
count++;
}
}
then you don't need to worry about trying to figure out what position you are at for the array.
You need to track the number of the elements:
int sum = 0;
for (int i = 0; i < num; i++){
for (int j = 0; j < total[i]; j++){
array[sum + j] = element[i];
}
sum += total[i];
}
Closed. This question does not meet Stack Overflow guidelines. It is not currently accepting answers.
Questions concerning problems with code you've written must describe the specific problem — and include valid code to reproduce it — in the question itself. See SSCCE.org for guidance.
Closed 9 years ago.
Improve this question
I am trying to augment a matrix with an identity matrix of similar dimensions, why is this bit of code not working?
It keeps giving the error 'vector subscript out of range'
for (i = 0; i < matrix.size(); i++)
for (j = matrix.size(); j < 2 * matrix.size(); j++)
if (i == j % matrix.size())
matrix[i][j] = 1;
else
matrix[i][j] = 0;
For a square matrix I think you are initialising j incorrectly?
for (i = 0; i < matrix.size(); i++)
for (j = 0; j < matrix.size(); j++)
if (i == j)
matrix[i][j] = 1;
else
matrix[i][j] = 0;
Edit: So to augment I think the following to extend the length of the rows
(http://en.wikipedia.org/wiki/Augmented_matrix)
for (i = 0; i < matrix.size(); i++)
matrix[i].resize(2 * matrix.size())
for (j = matrix.size(); j < 2 * matrix.size(); j++)
if (i == j % matrix.size())
matrix[i][j] = 1;
else
matrix[i][j] = 0;
You have to resize each row-vector (or row-array maybe) first. Otherwise the cell you try to access will be outside of your row range (and you receive the corresponding error).
You can do this by matrix[row].resize(2*matrix[row].size());, where row = 0 .. matrix.size()-1.