1 #include <iostream>
2 #include <cstring>
3 #include <stack>
4 #include <queue>
5 #include <cmath>
6 #include <exception>
7 #include <stdexcept>
8
9 using namespace std;
10
11 typedef struct Node {
12 int key;
13 struct Node *left;
14 struct Node *right;
15 }Node;
16
17
18 void PreOrder(Node* head) {
19 if(head) {
20 cout<<head->key<<"\t";
21 PreOrder(head->left);
22 PreOrder(head->right);
23 }
24 }
25
26 void InOrder(Node* head) {
27 if(head) {
28 InOrder(head->left);
29 cout<<head->key<<"\t";
30 InOrder(head->right);
31 }
32 }
33
34 void PostOrder(Node* head) {
35 if(head) {
36 PostOrder(head->left);
37 PostOrder(head->right);
38 cout<<head->key<<"\t";
39 }
40 }
41
42 void IterInOrder(Node* head) {
43 stack<Node*> ss;
44 Node* headCp = head;
45 for(;;) {
46 for(;headCp;headCp=headCp->left) {
47 ss.push(headCp);
48 }
49 if(ss.size()!=0) { // key point, if stack is of no item inside, top() will cause trouble.
50 headCp = ss.top();
51 ss.pop();
52 }
53 if(!headCp) {
54 break;
55 }
56 cout<<headCp->key<<"\t";
57 headCp = headCp->right;
58 }
59 }
60
61 void LevelOrder(Node* head) {
62 queue<Node*> que;
63 if(!head) {
64 return;
65 }
66 que.push(head);
67 for(;;) {
68 if(que.size()==0) {
69 break;
70 }
71 head = que.front();
72 que.pop();
73 if(head) {
74 cout<<head->key<<"\t";
75 if(head->left) {
76 que.push(head->left);
77 }
78 if(head->right) {
79 que.push(head->right);
80 }
81 }
82 }
83 }
84
85 Node* BuildTree(int* startPreorder, int* endPreorder, int* startInorder, int* endInorder);
86
87 Node* ConstructNewTree(int* PreOrderArr, int* InOrderArr, int length) {
88 if(PreOrderArr == NULL || InOrderArr == NULL || length == 0) {
89 return NULL;
90 } else {
91 int* startPreorder = PreOrderArr;
92 int* endPreorder = PreOrderArr+length-1;
93 int* startInorder = InOrderArr;
94 int* endInorder = InOrderArr+length-1;
95 return BuildTree(startPreorder,endPreorder,startInorder,endInorder);
96 }
97 }
98
99 Node* BuildTree(int* startPreorder, int* endPreorder, int* startInorder, int* endInorder) {
100 int rootValue = -1;
101 if(startPreorder == NULL || endPreorder==NULL || startInorder==NULL || endInorder==NULL) {
102 return NULL;
103 } else {
104 rootValue = *startPreorder;
105 }
106 Node* root = new Node();
107 root->key = rootValue;
108 root->left = NULL;
109 root->right = NULL;
110
111 if(startPreorder==endPreorder) {
112 if(startInorder==endInorder && *startPreorder == *startInorder) {
113 return root;
114 } else {
115 throw exception();
116 }
117 }
118
119 int* rootInorder = startInorder;
120 while(rootInorder<=endInorder && *rootInorder!=rootValue) {
121 rootInorder++;
122 }
123 if(*rootInorder!=rootValue) {
124 throw exception();
125 }
126 int leftLen = rootInorder-startInorder;
127 int righLen = endInorder-rootInorder;
128 int* leftPreorderEnd = startPreorder+leftLen;
129 if(leftLen>0) {
130 root->left = BuildTree(startPreorder+1,leftPreorderEnd,startInorder,rootInorder-1);
131 }
132 if(righLen>0) {
133 root->right = BuildTree(leftPreorderEnd+1,endPreorder,rootInorder+1,endInorder);
134 }
135 return root;
136 }
137
138
139 int main(int argc, char* argv[]) {
140 Node node1,node2,node3,node4,node5,node6,node7,node8;
141
142 node1.key = 1;
143 node1.left = &node2;
144 node1.right = &node3;
145
146 node2.key = 2;
147 node2.left = &node4;
148 node2.right = NULL;
149
150 node3.key = 3;
151 node3.left = &node5;
152 node3.right = &node6;
153
154 node4.key = 4;
155 node4.left = NULL;
156 node4.right = &node7;
157
158 node5.key = 5;
159 node5.left = NULL;
160 node5.right = NULL;
161
162 node6.key = 6;
163 node6.left = &node8;
164 node6.right = NULL;
165
166 node7.key = 7;
167 node7.left = NULL;
168 node7.right = NULL;
169
170 node8.key = 8;
171 node8.left = NULL;
172 node8.right = NULL;
173
174 cout<<"preorder:"<<endl;
175 PreOrder(&node1);
176 cout<<endl;
177
178 cout<<"inorder:"<<endl;
179 InOrder(&node1);
180 cout<<endl;
181
182
183 /*
184 cout<<"PreOrder:\n";
185 PreOrder(&node1);
186 cout<<endl;
187
188 cout<<"recursive InOrder:\n";
189 InOrder(&node1);
190 cout<<endl;
191
192 cout<<"loop InOrder:\n";
193 IterInOrder(&node1);
194 cout<<endl;
195
196 cout<<"PostOrder:\n";
197 PostOrder(&node1);
198 cout<<endl;
199
200 cout<<"Level Order:\n";
201 LevelOrder(&node1);
202 cout<<endl;
203 */
204
205 cout<<"start building the tree ..."<<endl;
206 int PreorderArr[] = {1,2,4,7,3,5,6,8};
207 int InorderArr[] = {4,7,2,1,5,3,8,6};
208 Node* root = ConstructNewTree(PreorderArr,InorderArr,sizeof(PreorderArr)/sizeof(int));
209 cout<<"build done."<<endl;
210
211 cout<<"preorder:"<<endl;
212 PreOrder(root);
213 cout<<endl;
214 cout<<"inorder:"<<endl;
215 InOrder(root);
216 cout<<endl;
217 cout<<"postorder:"<<endl;
218 PostOrder(root);
219 cout<<endl;
220
221 return 0;
222 }
