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);
		
		
	}
	
}