Java ，中序遍历
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public boolean isSymmetric(TreeNode root) {
ArrayList<int[]> tmp=new ArrayList<int[]>();
rec(root,tmp,0);
for(int i=0;i<tmp.size();i++)
{
if(tmp.get(i)[0]!=tmp.get(tmp.size()-1-i)[0]||tmp.get(i)[1]!=tmp.get(tmp.size()-1-i)[1])
return false;
}
return true;
}
public void rec(TreeNode root,List tmp,int level) {
if(root==null) return;
else
{
level++;
rec(root.left,tmp,level);
int[] m=new int[2];
m[0]=root.val;
m[1]=level;
tmp.add(m);
rec(root.right,tmp,level);
}
}
}
优解，Java
public boolean isSymmetric(TreeNode root) {
return root==null || isSymmetricHelp(root.left, root.right);
}
private boolean isSymmetricHelp(TreeNode left, TreeNode right){
if(left==null || right==null)
return left==right;
if(left.val!=right.val)
return false;
return isSymmetricHelp(left.left, right.right) && isSymmetricHelp(left.right, right.left);
}
