Interleave array in constant space

Question

I ran across the following sample job interview question. How can I solve it?

Suppose we have an array a1, a2,... , an, b1, b2, ..., bn.

The goal is to chan

Answer 1

It's called in-place in-shuffle problem. Here is its implementation in C++ based on here.

void in_place_in_shuffle(int arr[], int length)
{
    assert(arr && length>0 && !(length&1));

    // shuffle to {5, 0, 6, 1, 7, 2, 8, 3, 9, 4}
    int i,startPos=0;
    while(startPos3) i=i/3;

    return i;
}

---

Test:

int arr[] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};  
int length = sizeof(arr)/sizeof(int);
in_place_in_shuffle(arr, length);

After this, arr[] will be {0, 5, 1, 6, 2, 7, 3, 8, 4, 9}.