PAT甲级——A1066 Root of AVL Tree

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 N (≤) which is the total number of keys to be inserted. Then N distinct integer keys are given in the next line. All the numbers in a line are separated by a space.

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:

70

Sample Input 2:

7
88 70 61 96 120 90 65

Sample Output 2:

88

 #include <iostream>
 using namespace std;
 struct node {
     int val;
     struct node *left, *right;
 };
 node *rotateLeft(node *root) {
     node *t = root->right;
     root->right = t->left;
     t->left = root;
     return t;
 }
 node *rotateRight(node *root) {
     node *t = root->left;
     root->left = t->right;
     t->right = root;
     return t;
 }
 node *rotateLeftRight(node *root) {
     root->left = rotateLeft(root->left);
     return rotateRight(root);
 }
 node *rotateRightLeft(node *root) {
     root->right = rotateRight(root->right);
     return rotateLeft(root);
 }
 int getHeight(node *root) {
     if(root == NULL) return ;
     return max(getHeight(root->left), getHeight(root->right)) + ;
 }
 node *insert(node *root, int val) {
     if(root == NULL) {
         root = new node();
         root->val = val;
         root->left = root->right = NULL;
     } else if(val < root->val) {
         root->left = insert(root->left, val);
         if(getHeight(root->left) - getHeight(root->right) == )
             root = val < root->left->val ? rotateRight(root) : rotateLeftRight(root);
     } else {
         root->right = insert(root->right, val);
         if(getHeight(root->left) - getHeight(root->right) == -)
             root = val > root->right->val ? rotateLeft(root) : rotateRightLeft(root);
     }
     return root;
 }
 int main() {
     int n, val;
     scanf("%d", &n);
     node *root = NULL;
     for(int i = ; i < n; i++) {
         scanf("%d", &val);
         root = insert(root, val);
     }
     printf("%d", root->val);
     return ;
 }