Recursive Permutation C++ - c++

Question

I have problem with assignment, we need to implement recursive permutation in c++ for numbers.
Here is the code which is partly working, but missing some numbers.
I can't find where the problem is.
This code does work, but not exactly the right way.
This code take and array of number with size of that array.
in this case I am trying to solve the problem which appears when I send array longer than 3 numbers. If I send 3 numbers, output is:
///
1 2 3 /
1 3 2 /
3 1 2 /
2 1 3 /
2 3 1 /
3 2 1 /
Output in this case is correct. But when I set array to 4 and send size of it 4 I get:
///
1 2 3 4 /
1 2 4 3 /
1 4 2 3 /
4 1 2 3 /
**2 1 3 /
2 3 1 /
3 2 1 /**
3 2 1 4 /
3 2 4 1 /
3 4 2 1 /
4 3 2 1 /
Output is partly correct, but some numbers are missing.
Program should give output of all possible variations of numbers in array
#include <iostream>
using namespace std;
bool nextPermutation(int[],int);
void swap(int&, int&);
int Maxind(int[],int);
int Minind(int[],int);
void print (int[], int);
bool test (int[], int);
int fl=0;
int main() {
int a[]={1,2,3,4};
nextPermutation(a,4);
return 0;
}
void print(int a[], int s) {
for(int i=0; i<s; i++)
{
cout<<a[i]<<" ";
}
cout<<endl;
}
bool nextPermutation(int a[], int s)
{
int i=Maxind(a,s);
if(fl==0)
print(a,s);
if(i!=0) {
swap(a[i],a[i-1]);
nextPermutation(a,s);
}
else if(i==0 && test(a,s))
{
int p=a[0];
for(int i=0; i<=s-2; i++)
a[i]=a[i+1];
fl=1;
nextPermutation(a,s-1);
a[s-1]=p;
fl=0;
nextPermutation(a,s);
}
else
return false;
}
bool test (int a[], int s) {
if (Maxind(a,s)==0 && Minind(a,s)==s-1)
return false;
else
return true;
}
void swap(int& a, int& b)
{
int t=a; a=b; b=t;
}
int Maxind(int a[], int s)
{
int m=a[0], ind=0;
for(int i=0; i<s; i++)
if(m<a[i]) {
m=a[i];
ind=i;
}
return ind;
}
int Minind(int a[], int s)
{
int m=a[0], ind=0;
for(int i=0; i<s; i++)
if(m>a[i]) {
m=a[i];
ind=i;
}
return ind;
}

Answer 1

You need to send all numbers of possibilities for permutation.
If you change your main function you will get the solution. Add a loop in main funciton and send to nextPermutation(a, i) with variable i
int main() {
for(int i = 1; i < 5; i++) {
int a[]= {1,2,3,4};
nextPermutation(a,i);
}
return 0;
}
You should debug your program and also i figure out that your s value is decrasing here:
else if(i==0 && test(a,s)) {
int p=a[0];
for(int i=0; i<=s-2; i++) {
a[i]=a[i+1];
}
fl=1;
nextPermutation(a,s-1);
//*** careful you are decreasing s here and your output gives 3 numbers. !!***
a[s]=p;
fl=0;
nextPermutation(a,s);
}

Answer 2

I just modified the nextPermutation method of your code as follows and it worked.
bool nextPermutation(int a[], int s)
{
if(s == 0)
return false;
int i=Maxind(a,s);
if(fl==0)
print(a,s);
if(i!=0) {
swap(a[i],a[i-1]);
if(fl == 0)
nextPermutation(a,s);
else{
int temp = fl;
fl = 0;
nextPermutation(a,s+temp);
}
}
else if(i==0){
int p=a[0];
for(int i=0; i<=s-2; i++)
a[i]=a[i+1];
a[s-1]=p;
fl+=1;
nextPermutation(a,s-1);
}
else
return false;
}
Also I removed the methods test and Minind as they are not useful in my code.