PAT 甲级 1066. Root of AVL Tree (25)

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 (<=20) 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 ythe root of the resulting AVL tree in one line.

Sample Input 1:

588 70 61 96 120

Sample Output 1:

70

Sample Input 2:

788 70 61 96 120 90 65

Sample Output 2:

88

#include <iostream>#include <vector>#include <algorithm>#include <string>#include <set>using namespace std;struct node {int v, height;node *lchild, *rchild;}*root;node* newNode(int v) {node* Node = new node;Node->v = v;Node->height = 1;Node->lchild = Node->rchild = NULL;return Node;}int getHeight(node* root) {if (root == NULL) return 0;return root->height;}void updateHeight(node* root) {root->height = max(getHeight(root->lchild), getHeight(root->rchild))+1;}int getBalanceFactor(node* root) {return getHeight(root->lchild) - getHeight(root->rchild);}void L(node* &root) {node* temp = root->rchild;root->rchild = temp->lchild;temp->lchild = root;updateHeight(root);updateHeight(temp);root = temp;}void R(node* &root) {node* temp = root->lchild;root->lchild = temp->rchild;temp->rchild = root;updateHeight(root);  //为啥子一定要先更新rootupdateHeight(temp);root = temp;}void insert(node* &root, int v) {if (root == NULL) {root = newNode(v);return;}if (v < root->v) {insert(root->lchild, v);updateHeight(root);if (getBalanceFactor(root) == 2) {if (getBalanceFactor(root->lchild) == 1) {  //LL型R(root);}else if (getBalanceFactor(root->lchild) == -1) {  //LR型L(root->lchild);R(root);}}}else {insert(root->rchild, v);updateHeight(root);if (getBalanceFactor(root) == -2){if (getBalanceFactor(root->rchild) == -1) {L(root);}else if (getBalanceFactor(root->rchild) == 1) {R(root->rchild);L(root);}}}}node* create(int data[], int n) {node* root = NULL;for (int i = 0; i < n; i++) {insert(root, data[i]);}return root;}int main() {int n, v;scanf("%d", &n);for (int i = 0; i < n; i++) {scanf("%d", &v);insert(root, v);}printf("%d\n", root->v);return 0; }