101. 对称二叉树

package leetcode;

public class demo_101 {
    public boolean isSymmetric(TreeNode root) {
        if(root==null) {
            return true;
        }
        return function(root.left, root.right);
    }
    public boolean function(TreeNode left,TreeNode right) {
        //两个子节点都为空，则相等
        if(left==null&&right==null) {return true;}
        //两个子节点不相等，则不相等
        if(left==null&&right!=null||left!=null&&right==null||left.val!=right.val) {return false;}
        //左子树的左孩子与右孩子的右子树，左子树的右孩子与右孩子的左子树都相等，才相等
        return function(left.left, right.right)&function(left.right, right.left);     
    } 

}