题目链接

AVL-维基百科

/* Node is defined as :
typedef struct node
{
    int val;
    struct node* left;
    struct node* right;
    int ht;
} node; */

int Height(node *T)
{
    if (!T) return -1;         //In this question,NULL'height is -1
    return T->ht;
}

int Max(int a, int b)
{
    return a > b ? a : b;
}

node *SingleLeft(node *k1)		//单旋（RR）
{
    node *k2;
    k2 = k1->right;
    k1->right = k2->left;
    k2->left = k1;
    k1->ht = Max(Height(k1->left), Height(k1->right)) + 1;
    k2->ht = Max(Height(k2->left), Height(k2->right)) + 1;
    return k2;
}

node *SingleRight(node *k1)		//单旋（LL）
{
    node *k2;
    k2 = k1->left;
    k1->left = k2->right;
    k2->right = k1;
    k1->ht = Max(Height(k1->left), Height(k1->right)) + 1;
    k2->ht = Max(Height(k2->left), Height(k2->right)) + 1;
    return k2;
}

node *LeftRight(node *k1)		//双旋（LR）
{
    k1->left = SingleLeft(k1->left);
    return SingleRight(k1);
}

node *RightLeft(node *k1)		//双旋（RL）
{
    k1->right = SingleRight(k1->right);
    return SingleLeft(k1);
}

int BF(node *p)
{
    return Height(p->left) - Height(p->right);
}

node *insert(node *root, int val)
{
    if (!root)
    {
        root = (node *)malloc(sizeof(node));
        root->val = val;
        root->left = root->right = NULL;
        root->ht = 0;             //Leaf's height is 0
    }
    else
    {
        if (root->val < val)
        {
            root->right = insert(root->right, val);
            root->ht = Max(Height(root->left), Height(root->right)) + 1;
            if (BF(root) == -2)
            {
                if (val < root->right->val)		//RL
                {
                    root = RightLeft(root);
                }
                if (val > root->right->val)		//RR
                {
                    root = SingleLeft(root);
                }
            }
        }
        if (root->val > val)
        {
            root->left = insert(root->left, val);
            root->ht = Max(Height(root->left), Height(root->right)) + 1;
            if (BF(root) == 2)
            {
                if (val > root->left->val)		//LR
                {
                    root = LeftRight(root);
                }
                if (val < root->left->val)		//LL
                {
                    root = SingleRight(root);
                }
            }
        }
    }
    return root;
}

完整版
#include<stdio.h>				//Inserting of AVL tree
#include<stdlib.h>
#include<string.h>

typedef struct node
{
    int val;
    struct node *left;
    struct node *right;
    int ht;						//Height
}node;

int Height(node *T)
{
    if (!T) return 0;
    return T->ht;
}

int Max(int a, int b)
{
    return a > b ? a : b;
}

node *SingleLeft(node *k1)		//单旋（RR）
{
    node *k2;
    k2 = k1->right;
    k1->right = k2->left;
    k2->left = k1;
    k1->ht = Max(Height(k1->left), Height(k1->right)) + 1;
    k2->ht = Max(Height(k2->left), Height(k2->right)) + 1;
    return k2;
}

node *SingleRight(node *k1)		//单旋（LL）
{
    node *k2;
    k2 = k1->left;
    k1->left = k2->right;
    k2->right = k1;
    k1->ht = Max(Height(k1->left), Height(k1->right)) + 1;
    k2->ht = Max(Height(k2->left), Height(k2->right)) + 1;
    return k2;
}

node *LeftRight(node *k1)		//双旋（LR）
{
    k1->left = SingleLeft(k1->left);
    return SingleRight(k1);
}

node *RightLeft(node *k1)		//双旋（RL）
{
    k1->right = SingleRight(k1->right);
    return SingleLeft(k1);
}

int BF(node *p)
{
    return (Height(p->left) - Height(p->right));
}

node *insert(node *root, int val)
{
    if (!root)
    {
        root = (node *)malloc(sizeof(node));
        root->val = val;
        root->left = root->right = NULL;
        root->ht = 1;
    }
    else
    {
        if (root->val < val)
        {
            root->right = insert(root->right, val);
            root->ht = Max(Height(root->left), Height(root->right)) + 1;
            if (BF(root) == -2)
            {
                if (val < root->right->val)		//RL
                {
                    root = RightLeft(root);
                }
                if (val > root->right->val)		//RR
                {
                    root = SingleLeft(root);
                }
            }
        }
        if (root->val > val)
        {
            root->left = insert(root->left, val);
            root->ht = Max(Height(root->left), Height(root->right)) + 1;
            if (BF(root) == 2)
            {
                if (val > root->left->val)		//LR
                {
                    root = LeftRight(root);
                }
                if (val < root->left->val)		//LL
                {
                    root = SingleRight(root);
                }
            }
        }
    }
    return root;
}


node *Create()
{
    node *T;
    int val;
    T = NULL;
    scanf("%d", &val);
    while (val != -1)
    {
        T = insert(T, val);
        scanf("%d", &val);
    }
    return T;
}

void Inorder(node *T)
{
    if (T)
    {
        Inorder(T->left);
        printf("%d ", T->val);
        printf("%d   ", BF(T));
        Inorder(T->right);
    }
}

void Preorder(node *T)
{
    if (T)
    {
        printf("%d ", T->val);
        printf("%d   ", BF(T));
        Preorder(T->left);
        Preorder(T->right);
    }
}

int main()
{
    node *T;
    T = Create();			//test
    Inorder(T);
    printf("\n");
    Preorder(T);
    printf("\n");
    return 0;
}