101. Symmetric Tree

树相关的问题一般都是递归

public class Solution {

    public boolean isSymmetric(TreeNode root) {

        if(root==null)return true;

        return isMirror(root.left,root.right);

    }

    public boolean isMirror(TreeNode p,TreeNode q){

        if(p==null&&q==null)return true;

        if(p==null||q==null)return false;

        if(p.val==q.val&&isMirror(p.left,q.right)&&isMirror(p.right,q.left))return true;

        else return false;

    }

}