Connect Nodes at same level -- (Amazon)

1.cpp

// http://www.geeksforgeeks.org/connect-nodes-at-same-level/

void foo(t){
  if(!t) return;
  it(t -> left != NULL){
    if(t->right != NULL){
      t -> left -> next = t -> right;
    }
    else {
      if(t->next->left != NULL){
        t -> left -> next = t -> next -> left;
      }
      else if(t->next -> right != NULL){
        t -> left -> next = t -> next -> right;
      }
      else
        t -> left -> next = NULL;
    }
  }
  
  if(t->right != NULL){
    if(t->next != NULL){
      t -> right -> next = t -> next -> left;
    }
    else
      t -> right -> next = NULL;
  }
  foo(t->left);
  foo(t->right);
}