04对称二叉树

对称二叉树

给你一个二叉树的根节点 root ， 检查它是否轴对称。

示例 1：

输入：root = [1,2,2,3,4,4,3]
输出：true

示例 2：

输入：root = [1,2,2,null,3,null,3]
输出：false

提示：

• 树中节点数目在范围 [1, 1000] 内
• -100 <= Node.val <= 100

public class TreeNode {
  int val;
  TreeNode left;
  TreeNode right;

  TreeNode() {
  }

  TreeNode(int val) {
    this.val = val;
  }

  TreeNode(int val, TreeNode left, TreeNode right) {
    this.val = val;
    this.left = left;
    this.right = right;
  }
}

public boolean isSymmetric(TreeNode root) {
  return recur(root.left, root.right);
}

private boolean recur(TreeNode left, TreeNode right) {
  if (left == null && right == null) {
    return true;
  }
  if (left == null || right == null) {
    return false;
  }

  if (left.val != right.val) {
    return false;
  }
  return recur(left.left, right.right)
    && recur(left.right, right.left);


}