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;
}