leetcode_101

思路：
若左子树与右子树是镜像，需满足：
①根节点值相同
②左子树的左子树与右子树的右子树相同；左子树的右子树与右子树的左子树相同

代码：
/**

• Definition for a binary tree node.
• public class TreeNode {
• int val;
• TreeNode left;
• TreeNode right;
• TreeNode(int x) { val = x; }
• }
  */
  class Solution {
  public boolean isSymmetric(TreeNode root) {

  return isMirror(root,root);
  

  }
  public boolean isMirror(TreeNode t1,TreeNode t2){

  if(t1 == null && t2 == null){
      return true;
  }
  if(t1 == null || t2 == null){
      return false;
  }
  return (t1.val == t2.val) && (isMirror(t1.left,t2.right)) && (isMirror(t1.right,t2.left));
  

  }
  }