leetcode145——二叉树的后序遍历序列（非递归解法）

Posted 2023-02-19 dtwd886

题目链接：https://leetcode-cn.com/problems/binary-tree-postorder-traversal/submissions/

思路：以栈的方式来模拟

/**
 * 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:
    vector<int> postOrder(TreeNode* node)
    
        vector<int>result;
        stack<TreeNode* >stk;
        TreeNode* prev=nullptr;
        while(node||!stk.empty())
        
            while(node)
            
                stk.push(node);
                node=node->left;
            
            node=stk.top();
            stk.pop();
            if(node->right==nullptr||node->right==prev)
            
                result.push_back(node->val);
                prev=node;
                node=nullptr;
            
            else
             
                stk.push(node);
                node=node->right;
            
        
        return result;
    
    vector<int> postorderTraversal(TreeNode* root) 
        return postOrder(root);
        
    
;