PAT 1066. 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 (<=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:
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 treenode{
       int data,h;
       treenode* left=NULL;
       treenode* right=NULL;
};
using tree=treenode*;
int height(tree t){
    //cout<<"height(tree t)"<<endl;
    if(!t) return 0;
    return max(height(t->left),height(t->right))+1;
}
tree RotateLL(tree t){
    //cout<<" RotateLL(tree t)"<<endl;
    tree a=t->left;
    t->left=a->right;
    a->right=t;
    a->h=max(height(a->left),height(a->right))+1;
    t->h=max(height(t->left),height(t->right))+1;
    return a; 
}
tree RotateRR(tree t){
   //cout<<"RotateRR(tree t)"<<endl;
    tree a=t->right;
    t->right=a->left;
    a->left=t;
    a->h=max(height(a->left),height(a->right))+1;
    t->h=max(height(t->left),height(t->right))+1;
    return a; 
}
tree RotateLR(tree t){
//cout<<"RotateLR(tree t)"<<endl;
    t->left=RotateRR(t->left);
    return RotateLL(t);
}
tree RotateRL(tree t){
   //cout<<"RotateRL(tree t)"<<endl;
    t->right=RotateLL(t->right);
    return RotateRR(t);
}
tree insert(tree t,int v){
//cout<<" insert(tree t,int v)"<<endl;
    if(t==NULL){
       t=new treenode();
       t->data=v; t->h=0;
       return t;
    }else if(v<t->data){
       t->left=insert(t->left,v);
       if(height(t->left)-height(t->right)==2)
       if(v<t->left->data) 
       t=RotateLL(t);
       else t=RotateLR(t); 
    }else{
       t->right=insert(t->right,v);
       if(height(t->left)-height(t->right)==-2)
       if(v>t->right->data)
       t=RotateRR(t);
       else t=RotateRL(t); 
}
    t->h=height(t);
    return t;
} 
int main(){
    int n;
    cin>>n;
    tree t=NULL;
    for(int i=0;i<n;i++){
        int v; cin>>v;
        t=insert(t,v);
    }
    cout<<t->data<<endl;
    return 0;
}