binary-tree-postorder-traversal（后序遍历二叉树）

最新推荐文章于 2019-04-13 17:03:52 发布

原创最新推荐文章于 2019-04-13 17:03:52 发布 · 592 阅读

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文章标签：

#C++ #leetcode #二叉树 #遍历

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该博客主要介绍了如何非递归地解决LeetCode上的二叉树后序遍历问题。通过给出的例子，展示了对于给定的二叉树，如何返回其节点值的后序遍历序列。博主探讨了递归解决方案的直观性，并重点讨论了迭代实现的详细步骤。

题目描述

Given a binary tree, return the postorder traversal of its nodes' values.

For example:
Given binary tree{1,#,2,3},

return[3,2,1].

Note: Recursive solution is trivial, could you do it iteratively?

非递归实现：

语言：C++ 运行时间： <1 ms 占用内存：8568K 状态：答案正确

/**

 *
 Definition for binary tree

 *
 struct TreeNode {

 *    
 int val;

 *    
 TreeNode *left;

 *    
 TreeNode *right;

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

 *
 };

 */

class

Solution {

public:

    vector<int>
 postorderTraversal(TreeNode *root) {

        vector<int>
 v;

        stack<TreeNode*>
 s;

        map<TreeNode*,int>mp;//构造
  节点指针，访问flag 的map

        while

(root != NULL || !s.empty()){

            while

(root != NULL){

                s.push(root);

                mp[root]
 = 1;       //怎么记录flag？？？？

                root
 = root->left;

            }

            while

(!s.empty() && mp[s.top()]==2){

                v.push_back(s.top()->val);

                s.pop();

            }

            if

(!s.empty()){

                mp[s.top()]
 = 2;

                root
 = s.top()->right;

            }

        }

        return

v;

    }

};

添加笔记

/**

 *
 Definition for binary tree

 *
 struct TreeNode {

 *    
 int val;

 *    
 TreeNode *left;

 *    
 TreeNode *right;

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

 *
 };

*/

//=====================递归方法is
trivial。不过还是写出来吧=================================

class

Solution {

public:

    void

postOrder(TreeNode *root,vector<int>&vec){

        if(root
 != NULL){

            postOrder(root->left,vec);

            postOrder(root->right,vec);

            vec.push_back(root->val);

}

}

    vector<int>
 postorderTraversal(TreeNode *root) {

        vector<int>vec;

        postOrder(root,vec);

        return

vec;      

}

};