2021-11-09三种遍历顺序（前中后的非递归的遍历）

//三种常见的前中后序（非递归遍历）
//力扣算法
结构化解题思路
//前序遍历
/**

• Definition for a binary tree node.
• struct TreeNode {

• int val;
  

• TreeNode *left;
  

• TreeNode *right;
  

• TreeNode() : val(0), left(nullptr), right(nullptr) {}
  

• TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
  

• TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
  

• };
  /
  class Solution
  {
  public:
  void preorder(TreeNode root,vector&res)
  {
  if(root==nullptr)
  {
  return;
  }
  res.push_back(root->val);
  preorder(root->left,res);
  preorder(root->right,res);
  }
  vector preorderTraversal(TreeNode* root)
  {
  vector res;
  preorder(root,res);
  return res;
  }

};

//中序遍历
/**

• Definition for a binary tree node.
• struct TreeNode {

• int val;
  

• TreeNode *left;
  

• TreeNode *right;
  

• TreeNode() : val(0), left(nullptr), right(nullptr) {}
  

• TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
  

• TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
  

• };
  /
  class Solution {
  public:
  void inorder(TreeNode root,vector&res)
  {
  if(root==nullptr)
  {
  return;
  }
  inorder(root->left,res);
  res.push_back(root->val);
  inorder(root->right,res);
  }
  vector inorderTraversal(TreeNode* root)
  {
  vector res;
  inorder(root,res);
  return res;
  }
  };
  //后序遍历
  /**
• Definition for a binary tree node.
• struct TreeNode {

• int val;
  

• TreeNode *left;
  

• TreeNode *right;
  

• TreeNode() : val(0), left(nullptr), right(nullptr) {}
  

• TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
  

• TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
  

• };
  /
  class Solution {
  public:
  void postorder(TreeNoderoot,vector &res)
  {
  if(root==nullptr)
  {
  return;
  }
  postorder(root->left,res);
  postorder(root->right,res);
  res.push_back(root->val);
  }
  vector postorderTraversal(TreeNode* root)
  {
  vector res;
  postorder(root,res);
  return res;
  }
  };
  //总结：
  主要是根据的是根 左右 的顺序进行操作的过程。
  //来源于力扣的解析。