题目

题目描述	分别按照二叉树先序，中序和后序打印所有的节点。示例1	输入		{
   1,2,3}	返回值		[[1,2,3],[2,1,3],[2,3,1]]

解析

三次获取三种序列

/** * struct TreeNode { *	int val; *	struct TreeNode *left; *	struct TreeNode *right; * }; */class Solution {
   public:    /**     *      * @param root TreeNode类 the root of binary tree     * @return int整型vector
   
    <>>     */    vector
    
     
       > threeOrders(TreeNode* root) {
           // write code here        vector
      
       
        > res;        if(root==nullptr)return res;        vector
        
          preorder,inorder,postorder; preorder_traversal(preorder,root); inorder_traversal(inorder,root); postorder_traversal(postorder,root); res.push_back(preorder); res.push_back(inorder); res.push_back(postorder); return res; } void preorder_traversal(vector
         
          & v,TreeNode* root){ if(root==nullptr)return; v.push_back(root->val); preorder_traversal(v, root->left); preorder_traversal(v, root->right); } void inorder_traversal(vector
          
           & v,TreeNode* root){ if(root==nullptr)return; inorder_traversal(v, root->left); v.push_back(root->val); inorder_traversal(v, root->right); } void postorder_traversal(vector
           
            & v,TreeNode* root){ if(root==nullptr)return; postorder_traversal(v, root->left); postorder_traversal(v, root->right); v.push_back(root->val); } };

一次获取三种序列

class Solution {
   public:    void threeOrders(TreeNode* root, vector
   
    
      > &vect){
           if(!root)            return;        vect[0].push_back(root->val);        threeOrders(root->left,vect);        vect[1].push_back(root->val);        threeOrders(root->right,vect);        vect[2].push_back(root->val);    }    vector
     
      
        > threeOrders(TreeNode* root) {
           vector
       
        
          > vect = { { },{ },{ }}; threeOrders(root,vect); return vect; }};