/* * @lc app=leetcode.cn id=145 lang=cpp * * [145] 二叉树的后序遍历 */ // @lc code=start /** * 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: /* 迭代版本: 1、依次访问右子树,将右子树的各个节点采用头插法存储在数组中 2、当某个节点右子树为空时,该节点出栈,将此节点的左子树压入栈中,倘如左子树为空,访问当前节点的上一节点,如此循环即可 */ vector<int> postorderTraversal(TreeNode* root) { vector<int> res; if(root==nullptr) return res; stack<TreeNode*> record; while(!record.empty()|| root!=nullptr){ if(root){ record.push(root); res.insert(res.begin(),root->val); root=root->right; }else{ TreeNode* tmp=record.top(); record.pop(); root=tmp->left; } } return res; } }; // @lc code=end