leetcode-101-easy

Symmetric Tree
思路一: 递归

public boolean isSymmetric(TreeNode left, TreeNode right) {
   if (left == null && right == null) return true;
   if (left == null || right == null) return false;

   return left.val == right.val &&
           isSymmetric(left.left, right.right) &&
           isSymmetric(left.right, right.left);
}