1066 Root of AVL Tree (25 分)

An AVL tree is a self-balancing binary search tree. In an AVL tree, the heights of the two child subtrees of any node differ by at most one; if at any time they differ by more than one, rebalancing is done to restore this property. Figures 1-4 illustrate the rotation rules.

Now given a sequence of insertions, you are supposed to tell the root of the resulting AVL tree.

Input Specification:

Each input file contains one test case. For each case, the first line contains a positive integer

Output Specification:

For each test case, print the root of the resulting AVL tree in one line.

Sample Input 1:

5
88 70 61 96 120

Sample Output 1:

Sample Input 2:

7
88 70 61 96 120 90 65

Sample Output 2:

88

前面学完AVL这题就是板子题了。
只要插入就行，然后输出根节点。

 1 #include <iostream>
 2 #include <cmath>
 3 #include <vector>
 4 #include <algorithm>
 5 #include <queue>
 6 using namespace std;
 7 struct Node {
 8   int val;
 9   Node *left, *right;
10 } *tree;
11 int n, m;
12 
13 Node *leftrotate(Node * tree) {
14   Node *temp = tree->left;
15   tree->left = temp->right;
16   temp->right = tree;
17   return temp;
18 }
19 
20 Node *rightrotate(Node * tree) {
21   Node *temp = tree->right;
22   tree->right = temp->left;
23   temp->left = tree;
24   return temp;
25 }
26 
27 Node *rightleftrotate(Node * tree) {
28   tree->left = rightrotate(tree->left);
29   return leftrotate(tree);
30 }
31 
32 Node *leftrightrotate(Node * tree) {
33   tree->right = leftrotate(tree->right);
34   return rightrotate(tree);
35 }
36 
37 int getlen(Node * root) {
38   if (root == NULL)
39     return 0;
40   return max(getlen(root->left), getlen(root->right)) + 1;
41 }
42 Node *insert(Node * tree, int val) {
43   if (tree == NULL) {
44     tree = new Node();
45     tree->val = val;
46   } else if (val < tree->val) {
47     tree->left = insert(tree->left, val);
48     int ll = getlen(tree->left), rr = getlen(tree->right);
49     if (ll - rr >= 2) {
50       if (val < tree->left->val)
51         tree = leftrotate(tree);
52       else
53         tree = rightleftrotate(tree);
54     }
55   } else if (val > tree->val) {
56     tree->right = insert(tree->right, val);
57     int ll = getlen(tree->left), rr = getlen(tree->right);
58     if (rr - ll >= 2) {
59       if (val > tree->right->val)
60         tree = rightrotate(tree);
61       else
62         tree = leftrightrotate(tree);
63     }
64   }
65   return tree;
66 }
67 vector<int> v, vt;
68 void output(Node *root, int x){
69     if(root != NULL){
70         output(root->left, x<<1);
71           //cout <<root->val<<endl;
72         output(root->right, (x<<1)+1);
73     }else{
74         v.push_back(x);
75     }
76 }    
77 
78 int main() {
79   cin >> n;
80   for (int i = 0; i < n; i++) {
81     cin >> m;
82     tree = insert(tree, m);
83   }
84   cout << tree->val << endl;
85   return 0;
86 }