Question

find an algorithm for diameter of a tree in O(n).
the answer i find is this but i dont know how does it work.
int diameter2(TreeNode t, int* height)
{
int lh = 0, rh = 0;
int leftD = 0, rightD = 0;

if(t == NULL)
{
*height = 0;
return 0; /* diameter is also 0 */
}

leftD = diameter2(root->left, &lh);
rightD = diameter2(root->right,&rh);

/* Height of current node is max of heights of left and
right subtrees plus 1*/
*height = max(lh, rh) + 1;

return max(lh + rh + 1, leftD, rightD);
}
tnx for ur help.