平衡二叉树的4种旋转方法，高度以及插入代码

#include<iostream>
using namespace std;

struct node {
	int val;
	struct node *left;
	struct node *right;
};

//LL旋转
node *singleLeftRotation(node *root) {
	node *t = root->left;
	root->left = t->right;
	t->right = root;
	return t;
}

//RR旋转
node *singleRightRotation(node *root) {
	node *t = root->right;
	root->right = t->left;
	t->left = root;
	return t;
}

//LR旋转
node *doubleLeftRightRotation(node *root) {
	root->left = singleRightRotation(root->left);
	return singleLeftRotation(root);
}

//RL旋转
node *doubleRightLeftRotation(node *root) {
	root->right = singleLeftRotation(root->right);
	return singleRightRotation(root);
}

//高度检测
int getHeight(node *root) {
	if (root == NULL)
		return 0;
	return max(getHeight(root->left), getHeight(root->right)) + 1;
}

//平衡树插入
node *insert(node *root, int val) {
	if (root == NULL) { //为空就新建
		root = new node();
		root->val = val;
		root->left = NULL;
		root->right = NULL;
	} else if (val < root->val) {
		root->left = insert(root->left, val);
		if (getHeight(root->left) - getHeight(root->right) == 2) //如果比左结点还小就用LL旋转，反之用LR旋转
			root = val < root->left->val ? singleLeftRotation(root) : doubleLeftRightRotation(root);
	} else {
		root->right = insert(root->right, val);
		if (getHeight(root->left) - getHeight(root->right) == -2) //相应的右子树也是用RR或者RL
			root = val > root->right->val ? singleRightRotation(root) : doubleRightLeftRotation(root);
	}
	return root;
}