Check if two trees are identical?

bool IsIdentical(TreeNode p, TreeNode q) {

if (p == null && q == null) return true;

if (p == null || q == null) return false;

if (p.val != q.val) return false;

return IsIdentical(p.left, q.left) && IsIdentical(p.right,

q.right);

Explanation:

Recursive check values and structure for equality.