题解 | #实现二叉树先序，中序和后序遍历# 就这样写吧，直到天明

/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 * };
 */

class Solution {
public:
       vector<int>preRet;
       vector<int>inRet;
       vector<int>postRet;

    /**
     * 
     * @param root TreeNode类 the root of binary tree
     * @return int整型vector<vector<>>
     */
    void preorder(TreeNode* root) {
        if (!root) {
            return;
        }
        preRet.push_back(root->val);
        preorder(root->left);
        preorder(root->right);
    }
    
    void inorder(TreeNode* root) {
        if (!root) {
            return;
        }
        inorder(root->left);
        inRet.push_back(root->val);
        inorder(root->right);
    }
    
    void postorder(TreeNode* root) {
        if (!root) {
            return;
        }
        postorder(root->left);
        postorder(root->right);
        postRet.push_back(root->val);

    }
   
    vector<vector<int> > threeOrders(TreeNode* root) {
        
        preorder(root);
        inorder(root);
        postorder(root);
        cout << preRet.size() << endl;
        for (auto n : preRet) {
            cout << n << endl;
        }
        vector<vector<int>> ret (3, vector<int>(preRet.size(), 0));
        ret[0] = preRet;
        ret[1] = inRet;
        ret[2] = postRet;

        return ret;
        // write code here
    }
};