解析: 

boolean isSymmetrical(TreeNode pRoot) { if (pRoot == null) return true; return isSymmetrical(pRoot.left, pRoot.right); } boolean isSymmetrical(TreeNode t1, TreeNode t2) { if (t1 == null && t2 == null) return true; if (t1 == null || t2 == null) return false; if (t1.val != t2.val) return false; return isSymmetrical(t1.left, t2.right) && isSymmetrical(t1.right, t2.left); }