Permutation of integers from an array given lengh - algorithm

Question

I was interviewed a problem and after that I tested my code, found it wrong.
Not good at recursion. But I can't figure out the problem.
The question is: Given an array range from 0 ~ 9, and a length, for example, 3; generate
all permutations of integers from the given array in given length.
So, for the example:
The permutation should be: 012, 013, 014,..., 345, 346...
Below is my java code, where's the problem? (I think it's the index or the offset part)
And, if there's any better solution!
public void NumPermutation(int[] list, int offset, int[] temp, int index){
if(index == 4){
printarray(temp);
}
for(int count = offset; count < list.length; count++){
temp[index++] = list[count];
int te = list[offset];
list[offset] = list[count];
list[count] = te;
NumPermutation(list, offset, temp, index);
index -= 1;
}
}
public void test(int len){
int[] list = {0,1,2,3,4,5,6,7,8,9};
int[] temp = new int[4];
int index = 0, offset = 0;
NumPermutation(list, offset, temp,index);
}
The problem is that, the offset may increase each time and
it can't even reach the number to the end.

Answer 1

You need to:
Pass offset+1 to the recursive call.
Return in the if-statement.
Reverse your swap after the recursive call.
Replace the 4 with temp.length for a more generic solution.
Also preferably replace index++, index, index -= 1 with index, index + 1 and nothing.
Which results in this code: (replaced printarray with a standard print method, assuming this is Java)
public static void NumPermutation(int[] list, int offset, int[] temp, int index){
if(index == temp.length) {
System.out.println(Arrays.toString(temp));
return;
}
for(int count = offset; count < list.length; count++){
temp[index] = list[count];
// swap
int te = list[offset];
list[offset] = list[count];
list[count] = te;
NumPermutation(list, offset + 1, temp, index + 1);
// reverse swap
te = list[offset];
list[offset] = list[count];
list[count] = te;
}
}
Live demo.