LeetCode -- Symmetric Tree

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

For example, this binary tree is symmetric:

    1
   / \
  2   2
 / \ / \
3  4 4  3
But the following is not:
    1
   / \
  2   2
   \   \
   3    3

判断一个树的左右子树是否完全相等。
思路：分别对左右子树进行中序遍历，然后对遍历结果进行一一对比。

实现代码：

public class Solution {
public bool IsSymmetric(TreeNode root) {

if(root == null || root.left ==null && root.right == null){
return true;
}

var left = new List<string>();
var right = new List<string>();

TravelL(root.left, left);
TravelR(root.right, right);

if(left.Count != right.Count){
return false;
}

for(var i = 0;i < left.Count; i++){
if(left[i] != right[i]){
return false;
}
}

return true;
}

public void TravelL(TreeNode node , IList<string> result){

if(node == null){
result.Add("N");
return;
}

result.Add(node.val.ToString());
TravelL(node.left, result);
TravelL(node.right, result);

}
public void TravelR(TreeNode node , IList<string> result){

if(node == null){
result.Add("N");
return;
}

result.Add(node.val.ToString());
TravelR(node.right, result);
TravelR(node.left, result);

}

}