1 #include <vector>
2 #include <stack>
3 #include <queue>
4 using namespace std;
5
6
7 struct TreeNode{
8 int val;
9 TreeNode* left;
10 TreeNode* right;
11 TreeNode(int x):val(x),left(nullptr),right(nullptr){};
12 };
13
14 void preOrder(TreeNode* root,vector<int>& res){
15 if(root == nullptr) return;
16 res.push_back(root->val);
17 preOrder(root->left,res);
18 preOrder(root->right,res);
19 }
20
21 void inOrder(TreeNode* root,vector<int>& res){
22 if(root == nullptr) return;
23 inOrder(root->left,res);
24 res.push_back(root->val);
25 inOrder(root->right,res);
26 }
27
28 void postOrder(TreeNode* root,vector<int>& res){
29 if(root == nullptr) return;
30 postOrder(root->left,res);
31 postOrder(root->right,res);
32 res.push_back(root->val);
33 }
34
35
36 vector<int> preOrder(TreeNode* root){
37 vector<int> res;
38 if(root == nullptr) return res;
39
40 stack<TreeNode*> st;
41 TreeNode* cur = root;
42 while(cur || !st.empty()){
43 while(cur){
44 res.push_back(cur->val);
45 st.push(cur);
46 cur = cur->left;
47 }
48 if(!st.empty()){
49 cur = st.top();
50 st.pop();
51 cur = cur->right;
52 }
53 }
54 return res;
55 }
56
57
58 vector<int> inOrder(TreeNode* root){
59 vector<int> res;
60 if(root==nullptr) return res;
61
62 stack<TreeNode*> st;
63 TreeNode* cur = root;
64 while(cur || !st.empty()){
65 while(cur){
66 st.push(cur);
67 cur = cur->left;
68 }
69 if(!st.empty()){
70 cur = st.top();
71 st.pop();
72 res.push_back(cur->val);
73 cur = cur->right;
74 }
75 }
76 return res;
77 }
78
79
80 vector<int> postOrder(TreeNode* root){
81 vector<int> res;
82 if(root == nullptr) return res;
83
84 stack<TreeNode*> st;
85 TreeNode* cur = root;
86 while(cur){
87 st.push(cur);
88 cur = cur->left;
89 }
90
91 TreeNode* lastVisited = nullptr;
92 while(!st.empty()){
93 cur = st.top();
94 st.pop();
95 if(cur->right == nullptr || cur->right == lastVisited){
96 res.push_back(cur->val);
97 lastVisited = cur;
98 }else{
99 st.push(cur);
100 cur = cur->right;
101 while(cur){
102 st.push(cur);
103 cur = cur->left;
104 }
105 }
106 }
107 return res;
108 }
109
110 vector<int> levelOrder(TreeNode* root){
111 vector<int> res;
112 if(root == nullptr) return res;
113
114 queue<TreeNode*> q;
115 q.push(root);
116 while(!q.empty()){
117 size_t n = q.size();
118 for(size_t i=0;i<n;i++){
119 TreeNode* cur = q.back();
120 q.pop();
121 res.push_back(cur->val);
122 if(cur->left) q.push(cur->left);
123 if(cur->right) q.push(cur->right);
124 }
125 }
126 return res;
127 }
