OpenJudge 由中根顺序和后根序列重建二叉树

 1 #include <iostream>
 2 using namespace std;
 3 /*build BT from its inorder and postorder*/
 4 
 5 
 6 constexpr int MAXN = 65540;
 7 int postorder[MAXN], inorder[MAXN];
 8 
 9 struct btn
10 {
11     int data;
12     btn *left;
13     btn *right;
14 };
15 
16 btn *build_tree(int io1, int io2, int po1, int po2)
17 {
18     /*io1, io2 are the begining and ending points of inorder sequence respectively*/
19     /*po1, po2 are the begining and ending points of postorder sequence respectively*/
20     int i = 0, ion = io2 - io1 + 1;
21     btn* root = new btn;
22     root->data = postorder[po2];
23     root->left = NULL;
24     root->right = NULL;
25     for (i = 0; i < ion; i++) {
26         if (root->data == inorder[io1 + i])break;
27     }
28     if (i > 0) root->left = build_tree(io1, io1 + i - 1, po1, po1 + i - 1);
29     if (io1 + i < io2) root->right = build_tree(io1 + i + 1, io2, po1 + i, po2 - 1);
30     return root;
31 }
32 
33 void preorder(btn *root, int vnum, int &count)
34 {
35     if (root != NULL) {
36         cout << root->data;
37         if (count < vnum - 1) {
38             cout << " ";
39             count++;
40             preorder(root->left, vnum, count);
41             preorder(root->right, vnum, count);
42         }
43         else cout << endl;
44     }
45 }
46 
47 void deletetree(btn *root)
48 {
49     if (root != NULL) {
50         delete(root->left);
51         delete(root->right);
52         delete root;
53         root = NULL;
54     }
55 }
56 
57 int main()
58 {
59     int c = 0, i = 0, vnum = 0;
60     while (cin >> inorder[i++]) {
61         if (cin.get() != ‘ ‘)break;
62         /*Alththough cin will skip the blank space, the cursor stays at the blank after cin reads a number，thus cin.get() can fetch the 
63         blank space.*/
64     }
65 
66     vnum = i;
67     i = 0;
68     while (cin >> postorder[i++]) {
69         if (cin.get() != ‘ ‘)break;
70     }
71     btn *root = build_tree(0, i - 1, 0, i - 1);
72     preorder(root, vnum, c);
73     deletetree(root);
74     return 0;
75 }