Symmetric Tree

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isSymmetric(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<int> pre;
        vector<int> post;
        preTrav(pre, root);
        postTrav(post, root);
        return isSame(pre, post);
    }
    void preTrav(vector<int> & pre, TreeNode* r){
        if(r == NULL)
            return;
        else{
            preTrav(pre, r->right);
            pre.push_back(r->val);
            preTrav(pre, r->left);
        }
    }
    void postTrav(vector<int> & post, TreeNode* r){
        if(r == NULL)
            return;
        else{
            postTrav(post, r->left);
            post.push_back(r->val);
            postTrav(post, r->right);
        }
    }
    bool isSame(vector<int> & pre, vector<int> & post){
        for(int i = 0; i < post.size(); i++){
            if(pre[i] != post[i])
                return false;
        }
        return true;
    }
};