C++ - Strand sort using arrays only - c++

Question

I got a homework, to create a Strand sort algorithm in C++, but I'm not allowed to use lists, only arrays. I have trouble understanding the algorithm, because it was never explained to me, and Google yields limited information on this subject.
I've tried my best porting the code I found on Wikipedia, from PHP to C++, but It's not working correctly. It doesn't sort the array.
Here is my code, I know a lot of it is probably badly written, but it's the best I could do with my knowledge.
#include <iostream>
using namespace std;
void echoArray(int a[], int n) {
for(int i = 0; i < n; i++)
cout << a[i] << " ";
cout << endl;
}
//removes an element from array
int* array_remove(int* a, int& n, int index) {
int p = 0;
int* newArray = new int[n - 1];
for(int i = 0; i < n; i++) {
if(i != index) {
newArray[p] = a[i];
p++;
}
}
n--;
return newArray;
}
//adds an element to the end of an array
int* array_append(int* a, int& n, int el) {
int* newArray = new int[n+1];
int i = 0;
for(; i < n; i++) {
newArray[i] = a[i];
}
if(n == 0)
i = 0;
newArray[i] = el;
n++;
return newArray;
}
//inserts an element (el) to index p
int* array_insert(int* a, int& n, int p, int el) {
int c = 0;
n++;
int* newArray = new int[n];
for(int i = 0; i < n; i++) {
if(i != p) {
newArray[i] = a[c];
c++;
} else {
newArray[i] = el;
}
}
return newArray;
}
int* strandSort(int* a, int n) {
int arrC = n;
int resC = 0;
int subC = 0;
int* result = new int[1];
while(arrC > 0) {
subC = 0;
int* sublist = new int[1];
sublist = array_append(sublist, subC, a[0]);
a = array_remove(a, arrC, 0);
for(int i = 0; i < arrC; i++) {
if(a[i] > sublist[subC - 1]) {
sublist = array_append(sublist, subC, a[i]);
a = array_remove(a, arrC, i);
i--;
}
}
if(resC > 0) {
for(int i = 0; i < subC; i++) {
bool spliced = false;
for(int j = 0; j < resC - 1; i++) {
if(sublist[i] > result[j]) {
result = array_insert(result, resC, i, sublist[i]);
spliced = true;
break;
}
}
if(!spliced) {
result = array_append(result, resC, sublist[i]);
}
}
} else {
result = sublist;
resC = subC;
}
}
echoArray(result, resC);
return result;
}
int main() {
int a[] = {3, 20, 6, 1, 19, 21, 6, 11, 25, 6, 0, 1, 8, 7, 29, 26, 10, 29, 9, 5};
int n = 20;
strandSort(a, n);
return 0;
}
Also, I realize that arrays are passed by reference.

Answer 1

Use cout<< to target the problem
After read the wiki of Strand Sort, we know there is two parts of this algorithm.
Take out a relatively sorted list
Merge it with the result list
So you need to find which part is wrong, just add
cout << "step1: sublist = ";
echoArray(sublist, subC);
before if(resC > 0) { we will see step1 is right or wrong.
Add
cout << "step2: result = ";
echoArray(result, resC);
In the bottom of the while(arrC > 0) {} loop to check step2.
Get:
step1: sublist = 3 20 21 25 29
step2: result = 3 20 21 25 29
step1: sublist = 6 19 26 29
step2: result = 6 19 26 29 3 20 21 25 29
step1: sublist = 1 6 11
step2: result = 6 19 11 26 29 3 20 21 25 29
step1: sublist = 6 8 10
step2: result = 6 8 10 19 11 26 29 3 20 21 25 29
step1: sublist = 0 1 7 9
step2: result = 6 8 7 9 10 19 11 26 29 3 20 21 25 29
step1: sublist = 5
step2: result = 6 8 7 9 10 19 11 26 29 3 20 21 25 29 0
As we can see step1 is always right but the merge step is wrong.
So we will focus the code in if(resC > 0) {} block.
Read the code carefully
If you read your code carefully you will find in for(int j = 0; j < resC - 1; i++) { the i++ is nonsense.
And the merge step has many bugs, you need to rethink about it.
The fixed code of step 2:
if(resC > 0) {
int j = 0;
for(int i = 0; i < subC; i++) {
bool spliced = false;
for(;j < resC; j++) {
if(sublist[i] < result[j]) {
result = array_insert(result, resC, j++, sublist[i]);
spliced = true;
break;
}
}
if(!spliced) {
result = array_append(result, resC, sublist[i]);
}
}
} else {
result = sublist;
resC = subC;
}