Leetcode-Symmetric Tree

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree [1,2,2,3,4,4,3] is symmetric:

    1
    / \
  2   2
 / \ / \
3  4 4  3
But the following [1,2,2,null,3,null,3] is not:
    1
   / \
  2   2
   \   \
   3    3

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    void mirror(TreeNode* root){
        if(root==NULL) return;
        swap(root->left,root->right);
        mirror(root->left);
        mirror(root->right);
    }
    void preOrder(TreeNode* root,vector<int> &result){
        if(root==NULL) return;
        result.push_back(root->val);
        preOrder(root->left,result);
        preOrder(root->right,result);
    }
    void inOrder(TreeNode* root,vector<int> &result){
        if(root==NULL) return;
        inOrder(root->left,result);
        result.push_back(root->val);
        inOrder(root->right,result);
    }
    bool equalVector(vector<int> first, vector<int> second){
        if(first.size()!=second.size()) return false;
        for(int i=0;i<first.size();i++){
            if(first[i]!=second[i])
            return false;
        }
        return true;
    }
    bool equalTree(TreeNode* left, TreeNode* right){
        vector<int> l_pre,l_in,r_pre,r_in;
        preOrder(left,l_pre);
        inOrder(left,l_in);
        preOrder(right,r_pre);
        inOrder(right,r_in);
        return equalVector(l_pre,r_pre)&&equalVector(l_in,r_in);
    }
    bool isSymmetric(TreeNode* root) {
        if(root==NULL) return true;
        mirror(root->right);
        return equalTree(root->left,root->right);
    }
};

以上方法雖然通過，但是有bug
bug用例
[1,1]
[1,null,1]

錯誤在與我判斷兩棵樹是否相同的時候，用了 “兩棵樹的preorder & inorder 一致的話，則兩棵樹相等”，實際上有問題的，當節點的值相等，則此法無效。

正確做法如下：

 bool isSameTree(TreeNode* p, TreeNode* q) {
        if(p==NULL && q==NULL) return true;
        if(p!=NULL && q==NULL) return false;
        if(p==NULL && q!=NULL) return false;
        return (p->val==q->val) && isSameTree(p->left,q->left) && isSameTree(p->right,q->right) ;
    }