serialize and deserialize a binary tree

serialize(a, list)
{
static int level = 0;
if(!a)
{
list[level++] = -1;
return
}

list[level++] = a->num;

serialize(a->left, list)
serialize(a->right, list)
}

deserialize(a, list)
{
static int level = 0;

if(list[level] == -1)
{
level++
return 0
}

a = createNode()
a->num = list[level++]
a->left = deserialize(a, list)
a->right = deserialize(a, list)
}