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) {}
 * };
 */
#include <vector>
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> v1;
        vector<int> v2;
        vector<int> v3;
    vector<vector<int> > threeOrders(TreeNode* root) {
        // write code here
       
        if(root!=nullptr){
        preorder(root);
        midorder(root);
        postorder(root);
        

            }
        vector<vector<int>> ans;
        ans.push_back(v1);
        ans.push_back(v2);
        ans.push_back(v3);
        return ans;
     }
    void preorder(TreeNode* root){
        if(root==nullptr){
            return ;
        }
        v1.push_back(root->val);//先向vector容器中插入中，插入顺序是中左右
        preorder( root->left);
        preorder(root->right);
    }
     void midorder(TreeNode* root){
        if(root==nullptr){
            return ;
        }
       
        midorder( root->left);
         v2.push_back(root->val);
        midorder(root->right);
    }
    void postorder(TreeNode* root){
        if(root==nullptr){
            return ;
        }
       
        postorder( root->left);
        
        postorder(root->right);
         v3.push_back(root->val);
    }
     
};