题解 | #实现二叉树先序，中序和后序遍历#

/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 *	TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 the root of binary tree
     * @return int整型vector<vector<>>
     */
    vector<int>pre;
    vector<int>mid;
    vector<int>post;
    vector<vector<int> > threeOrders(TreeNode* root) {
        // write code here
        if(root != NULL)
        {
            preorder(root);
            midorder(root);
            postorder(root);
        }
        vector<vector<int>>res = {pre, mid, post};
        return res;
    }
    void preorder(TreeNode* root)
    {
        if(root == NULL)return;
        pre.push_back(root->val);
        preorder(root->left);
        preorder(root->right);
    }
    void midorder(TreeNode* root)
    {
        if(root == NULL)return;
        midorder(root->left);
        mid.push_back(root->val);
        midorder(root->right);
    }
    void postorder(TreeNode* root)
    {
        if(root == NULL)
        return;
        postorder(root->left);
        postorder(root->right);
        post.push_back(root->val);
    }
};