binary_tree_postorder
binary_tree_postorder.cpp 源码
// 二叉树的后序遍历
#include "vector"
#include "stack"
using namespace std;
struct TreeNode {
int val;
TreeNode *left;
TreeNode *right;
TreeNode() {}
TreeNode(int val) : val(val) {}
TreeNode(int val, TreeNode *left, TreeNode *right) : val(val), left(left), right(right) {}
};
class Solution {
public:
// 递归
vector<int> postorderTraversal1(TreeNode* root) {
vector<int> res;
helper(root, res);
return res;
}
void helper(TreeNode* root, vector<int> &res) {
if (!root) {
return;
}
helper(root->left, res);
helper(root->right, res);
res.push_back(root->val);
}
// 迭代
vector<int> postorderTraversal1(TreeNode* root) {
vector<int> res;
if (root == nullptr) {
return res;
}
stack<TreeNode*> s;
s.push(root);
while (!s.empty()) {
TreeNode* node = s.top();
s.pop();
res.insert(res.begin(), node->val);
if (node->left) {
s.push(node->left);
}
if (node->right) {
s.push(node->right);
}
}
return res;
}
};
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