pat 1066 Root of AVL Tree (25)

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典型的AVL的插入旋轉問題見博客

主要注意四種方式下 中間節點的左右孩子到底應該怎麼變換.

#include<bits/stdc++.h>

using namespace std;
const int maxn = 25;
struct node
{
    node * l;
    node * r;
    int value;
    node()
    {
        l = r = nullptr;
    }
};
int get_height(node *root)
{
    if(root == nullptr)
        return 0;
    return max(get_height(root -> l) ,get_height(root -> r)) + 1;
}
node* LL(node *root)
{
    node *tmp;
    tmp = root -> l;
    root -> l = tmp -> r;
    tmp -> r = root;
    return tmp;
}
node* RR(node *root)
{
    node *tmp;
    tmp = root -> r;
    root -> r = tmp -> l;
    tmp -> l = root;
    return tmp;
}
node* LR(node *root)
{
    root -> l = RR(root -> l);
    return LL(root);
}
node *RL(node *root)
{
    root -> r = LL(root -> r);
    return RR(root);
}
node* Insert(node *root,int value)
{
    if(root == nullptr)
    {
        node *tmp = new node;
        tmp -> value = value;
        return tmp;
    }
    else if(value < root -> value)
    {
        root -> l = Insert(root -> l,value);
        if(get_height(root -> l) - get_height(root -> r) == 2)
        {
            if(value < root -> l -> value)
                root = LL(root);
            else
                root = LR(root);
        }
    }
    else
    {
        root -> r =  Insert(root -> r,value);
        if(get_height(root -> r) - get_height(root -> l) == 2)
        {
            if(value < root -> r -> value)
                root = RL(root);
            else
                root = RR(root);
        }
    }
    return root;
}
int main()
{
    int n;
    scanf("%d",&n);
    node *root = nullptr;
    for(int i = 1;i <= n;++i)
    {
        int a;
        scanf("%d",&a);
        root = Insert(root,a);
    }
    printf("%d\n",root -> value);
}

#include<bits/stdc++.h>

using namespace std;
const int maxn = 25;
struct node
{
    node * l;
    node * r;
    int value;
    node()
    {
        l = r = nullptr;
    }
};
int get_height(node *root)
{
    if(root == nullptr)
        return 0;
    return max(get_height(root -> l) ,get_height(root -> r)) + 1;
}
node* LL(node *root)
{
    node *tmp;
    tmp = root -> l;
    root -> l = tmp -> r;
    tmp -> r = root;
    return tmp;
}
node* RR(node *root)
{
    node *tmp;
    tmp = root -> r;
    root -> r = tmp -> l;
    tmp -> l = root;
    return tmp;
}
node* LR(node *root)
{
    root -> l = RR(root -> l);
    return LL(root);
}
node *RL(node *root)
{
    root -> r = LL(root -> r);
    return RR(root);
}
node* Fix(node* root)
{
    int lheight = get_height(root -> l);
    int rheight = get_height(root -> r);
    if(lheight > rheight)
    {
        if(get_height(root -> l -> l) > get_height(root -> l -> r))
            root = LL(root);
        else
            root = LR(root);

    }
    else
    {
        if(get_height(root -> r -> l) > get_height(root -> r -> r))
            root = RL(root);
        else
            root = RR(root);
    }
    return root;
}
node* Insert(node *root,int value)
{
    if(root == nullptr)
    {
        node *tmp = new node;
        tmp -> value = value;
        return tmp;
    }
    else if(value < root -> value)
    {
        root -> l = Insert(root -> l,value);
        if(get_height(root -> l) - get_height(root -> r) == 2)
            root = Fix(root);
    }
    else
    {
        root -> r =  Insert(root -> r,value);
        if(get_height(root -> r) - get_height(root -> l) == 2)
            root = Fix(root);
    }
    return root;
}
int main()
{
    int n;
    scanf("%d",&n);
    node *root = nullptr;
    for(int i = 1;i <= n;++i)
    {
        int a;
        scanf("%d",&a);
        root = Insert(root,a);
    }
    printf("%d\n",root -> value);
}