题目：

前：

中：

后：

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代码（首刷自解 2024年1月24日）：

//前序遍历，递归
class Solution {
public:void funcOfRecursion(TreeNode* cur, vector<int>& vec) {if (cur == nullptr) return;vec.emplace_back(cur->val);funcOfRecursion(cur->left,vec);funcOfRecursion(cur->right,vec);}vector<int> preorderTraversal(TreeNode* root) {vector<int> vec = {};if (root == nullptr) return vec;funcOfRecursion(root,vec);return vec; }
};

//中序遍历，递归
class Solution {
public:void funcOfRecursion(TreeNode* cur,vector<int>& vec) {if(cur == nullptr) return;funcOfRecursion(cur->left,vec);vec.emplace_back(cur->val);funcOfRecursion(cur->right,vec);}vector<int> inorderTraversal(TreeNode* root) {vector<int> vec = {};if(root == nullptr) return vec;funcOfRecursion(root,vec);return vec;}
};

//后序遍历，递归
class Solution {
public:void funcOfRecursion(TreeNode* cur, vector<int>& vec) {if(cur == nullptr) return;funcOfRecursion(cur->left,vec);funcOfRecursion(cur->right,vec);vec.emplace_back(cur->val);}vector<int> postorderTraversal(TreeNode* root) {vector<int> vec = {};if(root == nullptr) return vec;funcOfRecursion(root,vec);return vec;}
};

//前序遍历，迭代
class Solution {
public:vector<int> preorderTraversal(TreeNode* root) {vector<int> res = {};if(root == nullptr) return res;stack<TreeNode*> st;TreeNode* cur = root;st.push(cur);while (!st.empty()) {TreeNode* node = st.top();st.pop();res.emplace_back(node->val);if(node->right) st.push(node->right);if(node->left) st.push(node->left);}return res;}
};

//中序遍历，迭代
class Solution {
public:vector<int> inorderTraversal(TreeNode* root) {vector<int> res = {};if(root == nullptr) return res;stack<TreeNode*> st;TreeNode* cur = root;while (!st.empty() || cur != NULL) {if (cur != nullptr) {st.push(cur);cur = cur -> left;} else {cur = st.top();res.emplace_back(cur->val);st.pop();cur = cur -> right;}}return res;}
};

//后序遍历 迭代
class Solution {
public:vector<int> postorderTraversal(TreeNode* root) {vector<int> res = {};if(root == nullptr) return res;stack<TreeNode*> st;TreeNode* cur = root;st.push(cur);while (!st.empty()) {TreeNode* node = st.top();st.pop();res.emplace_back(node->val);if(node->left) st.push(node->left);if(node->right) st.push(node->right);}reverse(res.begin(),res.end());return res;}
};