这道题类似1123题。

#include <cstdio>
#include <algorithm>

struct node{
    int key;
    node* left = nullptr;
    node* right = nullptr;
};

int N, t;
node* root = nullptr;

int getHeight(node* r){
    if(!r){
        return 0;
    }
    return std::max(getHeight(r->left), getHeight(r->right)) + 1;
}

node* LLRotation(node* r){
    node* tmp = r->left;
    r->left = r->left->right;
    tmp->right = r;
    return tmp;
}

node* RRRotation(node* r){
    node* tmp = r->right;
    r->right = r->right->left;
    tmp->left = r;
    return tmp;
}

node* LRRotation(node* r){
    r->left = RRRotation(r->left);
    return LLRotation(r);
}

node* RLRotation(node* r){
    r->right = LLRotation(r->right);
    return RRRotation(r);
}

node* insertKey(node* r, int key){
    if(!r){
        node* tmp = new node;
        tmp->key = key;
        r = tmp;
        return r;
    }
    if(key < r->key){
        r->left = insertKey(r->left, key);
        if(getHeight(r->left) - getHeight(r->right) == 2){
            if(key < r->left->key){
                r = LLRotation(r);
            } else{
                r = LRRotation(r);
            }
        }
    } else{
        r->right = insertKey(r->right, key);
        if(getHeight(r->right) - getHeight(r->left) == 2){
            if(key < r->right->key){
                r = RLRotation(r);
            } else{
                r = RRRotation(r);
            }
        }
    }
    return r;
}

int main(){
    scanf("%d", &N);
    for(int i = 0; i < N; ++i){
        scanf("%d", &t);
        root = insertKey(root, t);
    }
    printf("%d", root->key);
    return 0;
}

题目如下：

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 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