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145.binary-tree-postorder-traversal.cpp
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145.binary-tree-postorder-traversal.cpp
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/*
* @lc app=leetcode id=145 lang=cpp
*
* [145] Binary Tree Postorder Traversal
*/
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
// 深度优先:递归
// void help(TreeNode* root, vector<int>& ret) {
// if (!root) {
// return;
// }
// help(root->left, ret);
// help(root->right, ret);
// ret.push_back(root->val);
// }
// vector<int> postorderTraversal(TreeNode* root) {
// if (!root) {
// return vector<int>();
// }
// vector<int> ret;
// help(root, ret);
// return ret;
// }
// 深度优先:迭代
// 妙啊,后序遍历是从前面insert的
vector<int> postorderTraversal(TreeNode* root) {
if (!root) {
return vector<int>();
}
vector<int> ret;
stack<TreeNode*> s;
s.push(root);
while (!s.empty()) {
auto r = s.top();
s.pop();
ret.insert(ret.begin(), r->val);
if (r->left) {
s.push(r->left);
}
if (r->right) {
s.push(r->right);
}
}
return ret;
}
};