# BST(二叉搜尋樹、二叉查找樹、二叉排序樹)
定義:
1、要麼是一棵空樹
2、如果不為空,那麼其左子樹節點的值都小于根節點的值;右子樹節點的值都大于根節點的值
3、其左右子樹也是二叉搜尋樹
#
定義:
平衡二叉樹(Balanced Binary Tree)又被稱為AVL樹(有别于AVL算法),且具有以下性質:它是一 棵空樹或它的左右兩個子樹的高度差的絕對值不超過1,并且左右兩個子樹都是一棵平衡二叉樹。平衡二叉樹的常用算法有紅黑樹、AVL、Treap、伸展樹等。
最小不平衡子樹: 以離插入結點最近、且平衡因子絕對值大于 1 的結點作根結點的子樹。
調整該子樹的分為四種情況:
(1)LL形
(2)LR形
(3)RR形
(4)RL形
代碼實作:
LR:
RL:
#include<stdio.h>
#include<iostream>
using namespace std;
#define FALSE 0
#define TRUE 1
typedef struct {
int key;
} element;
typedef struct tree_node {
struct tree_node *left_child;
element data;
short bf;
struct tree_node *right_child;
} tree_node, *tree_pointer;
int unbalanced = FALSE;
tree_pointer root = NULL;
void left_rotation(tree_pointer *parent, int *unbalanced);
void right_rotation(tree_pointer *parent, int *unbalanced);
void avl_insert(tree_pointer *parent, element x, int *unbalanced);
/*
*1.如果要插入的元素的父節點為空則為其配置設定記憶體并處理
*2.如果小于父節點的資料域則插入父節點的左孩子,并旋轉
*3.如果大于父節點的資料域則插入父節點的右孩子,并旋轉
*/
void avl_insert(tree_pointer *parent, element x, int *unbalanced) {
if(!*parent) {
*unbalanced = TRUE;
*parent = new tree_node();
(*parent)->left_child = (*parent)->right_child = NULL;
(*parent)->bf = 0;
(*parent)->data = x;
}
else if(x.key < (*parent)->data.key) {
avl_insert(&(*parent)->left_child, x, unbalanced);
if(*unbalanced) {
/*
* unbalanced表示是插完之後就不平衡了 和 判斷還用不用處理平衡因子
*/
switch((*parent)->bf) {
case -1:
(*parent)->bf = 0;
*unbalanced = FALSE;
break;
case 0:
(*parent)->bf = 1;
break;
case 1:
left_rotation(parent,unbalanced);
}
}
}
else if(x.key > (*parent)->data.key) {
avl_insert(&(*parent)->right_child, x, unbalanced);
if(*unbalanced) {
switch((*parent)->bf) {
case 1:
(*parent)->bf = 0;
*unbalanced = FALSE;
break;
case 0:
(*parent)->bf = 1;
break;
case -1:
right_rotation(parent, unbalanced);
}
}
}
else {
*unbalanced = FALSE;
printf("該元素已經存在!\n");
}
}
void left_rotation(tree_pointer *parent, int *unbalanced) {
tree_pointer grand_child, child;
child = (*parent)->left_child;
if(child->bf == 1) {
//LL
(*parent)->left_child = child->right_child;
child->right_child = *parent;
(*parent)->bf = 0;
(*parent) = child;
} else {
//LR
grand_child = child->right_child;
child->right_child = grand_child->left_child;
grand_child->left_child = child;
(*parent)->left_child = grand_child->right_child;
grand_child->right_child = (*parent);
switch(grand_child->bf) {
case 1:
(*parent)->bf = -1;
child->bf = 0;
case 0:
(*parent)->bf = child->bf = 0;
case -1:
(*parent)->bf = 0;
child->bf = 1;
}
(*parent) = grand_child;
}
(*parent)->bf = 0;
*unbalanced = FALSE;
}
void right_rotation(tree_pointer *parent, int *unbalanced) {
tree_pointer grand_child, child;
child = (*parent)->right_child;
if(child->bf == -1) {
//RR
(*parent)->right_child = child->left_child;
child->left_child = (*parent);
(*parent) = child;
} else {
//RL
grand_child = child->left_child;
child->left_child = grand_child->right_child;
grand_child->right_child = child;
(*parent)->right_child = grand_child->left_child;
grand_child->left_child = (*parent);
switch(grand_child->bf) {
case 1:
(*parent)->bf = 0;
child->bf = -1;
case 0:
(*parent)->bf = child->bf = 0;
case -1:
(*parent)->bf = 1;
child->bf = 0;
}
(*parent) = grand_child;
}
(*parent)->bf = 0;
*unbalanced = FALSE;
}
void raverse(tree_pointer root) {
if(root) {
printf("%d ",root->data.key);
raverse(root->left_child);
raverse(root->right_child);
}
}
int main() {
int arr[11] = {15,6,18,3,7,17,20,2,4,13,9};
element arr_x[11];
for(int i = 0; i<11; i++) {
arr_x[i].key = arr[i];
// cout<<arr_x[i].key<<endl;
avl_insert(&root, arr_x[i], &unbalanced);
}
raverse(root);
printf("\n");
return 0;
}