Using the binary_tree_node, write a recursive function to meet the following specification. Check as much of the precondition as possible.

template

void flip(binary_tree_node* root_ptr)

// Precondition: root_ptr is the root pointer of a non-empty binary tree.

// Postcondition: The tree is now the mirror image of its original value.

// Example original tree: Example new tree:

// 1 1

// / \ / \

// 2 3 3 2

// / \ / \

// 4 5 5 4