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;
    void Preamble(TreeNode* root) {
        if (root == nullptr)
            return ;
        pre.push_back(root->val);
        Preamble(root->left);
        Preamble(root->right);
    }
    void Middle(TreeNode* root) {
        if (root == nullptr)
            return ;
        Middle(root->left);
        mid.push_back(root->val);
        Middle(root->right);
    }
    void Post(TreeNode* root ) {
        if (root == nullptr)
            return ;
        Post(root->left);
        Post(root->right);
        post.push_back(root->val);
    }
    vector<vector<int> > threeOrders(TreeNode* root) {
        // write code here
        if(root!=nullptr)
        {
            Preamble(root);
            Middle(root);
            Post(root);
        }
        vector<vector<int>>res={pre,mid,post};
        return res;
    }
};