Interview question: If [a1,a2,a3...,an,b1,b2...bn] is given input change this to [a1,b1,a2,b2.....an,bn] , solution should be in-place

Two solutions:
1. Swap middle pair, and keep swapping increasing number of pairs from the middle:

C++ implementation:

void arrangeArray(int *a){

int num_swaps = 1; //number of swaps to be done

int i = 0;

int mid=0;

int swap_start_idx = 0;

int swap_end_idx = 0;

int temp=0;

//find lenght of array

while(a[i] != '\0'){

i++;

}

mid = i/2 -1;

cout << "mid: " << mid << endl;

i=0;

while(a[i] != '\0'){

cout << a[i] << endl;

i++;

}

while(mid -num_swaps +1 > 0){

swap_start_idx = mid-num_swaps+1;

swap_end_idx = mid+num_swaps;

//cout << "num_swaps: " << num_swaps << " swap_start_idx " << swap_start_idx << "  swap_end_idx "<< swap_end_idx << endl;

while(swap_end_idx > swap_start_idx){

temp=a[swap_start_idx];

a[swap_start_idx]=a[swap_start_idx+1];

a[swap_start_idx+1] = temp;

//cout << "a[swap_start_idx]: " <<  a[swap_start_idx] << "  a[swap_end_idx]: " << a[swap_end_idx] << endl; 

swap_start_idx += 2;

}

num_swaps++;

//cout << "num_swaps" << num_swaps << endl;

}

return;

}

int main () {

    int a[] = {1,3,5,7,2,4,6,8};

int i=0;

while(a[i] != '\0'){

cout << a[i] << endl;

i++;

}

arrangeArray(a);

i=0;

while(a[i] != '\0'){

cout << a[i] << endl;

i++;

}

 return 0;

}