101. Symmetric Tree

Given a binary tree, check whether it is a mirror of the itself (ie, symmetric around its center).

For example, this binary tree is symmetric:

    1   /   2   2/\/3  4 4  3

But the following are not:

    1   /   2   2   \      3    3
The code is as follows:

1 /**2 * Definition for a binary tree node.3 * public class TreeNode {4 * int val;5 * TreeNode left;6 * TreeNode right;7 * TreeNode (int x) {val = x;}8  * }9  */Ten  Public classSolution { One      Public Booleanissymmetric (TreeNode root) { A         if(root==NULL) -         return true; -TreeNode left=Root.left; theTreeNode right=Root.right; -          -         if(Lefttraverse (left). Equals (Righttraverse (right))) -         return true; +          -         return false; +     } A      PublicList<string>lefttraverse (TreeNode root) { atList<string> list=NewArraylist<>(); -         if(root==NULL) -         returnlist; -          - List.add (string.valueof (Root.val)); -         if(root.left!=NULL) in List.addall (Lefttraverse (Root.left)); -         Else toList.add (""); +          -         if(root.right!=NULL) the List.addall (Lefttraverse (root.right)); *         Else $List.add ("");Panax Notoginseng         returnlist; -     } the       PublicList<string>righttraverse (TreeNode root) { +List<string> list=NewArraylist<>(); A         if(root==NULL) the         returnlist; +          - List.add (string.valueof (Root.val)); $         if(root.right!=NULL) $ List.addall (Righttraverse (root.right)); -         Else -List.add (""); the          -         if(root.left!=NULL)Wuyi List.addall (Righttraverse (Root.left)); the         Else -List.add (""); Wu          -           About         returnlist; $     } -}

101. Symmetric Tree