04-树5 Root of AVL Tree--------C语言

An AVL tree is a self-balancing binary search tree. In an AVL tree, the heights of the two child subtrees of any node differ by at most one; if at any time they differ by more than one, rebalancing is done to restore this property. Figures 1-4 illustrate the rotation rules.

Now given a sequence of insertions, you are supposed to tell the root of the resulting AVL tree.

Input Specification:

Each input file contains one test case. For each case, the first line contains a positive integer N (≤20) which is the total number of keys to be inserted. Then N distinct integer keys are given in the next line. All the numbers in a line are separated by a space.

Output Specification:

For each test case, print the root of the resulting AVL tree in one line.

Sample Input 1:

5
88 70 61 96 120

结尾无空行

Sample Output 1:

70

结尾无空行

Sample Input 2:

7
88 70 61 96 120 90 65

Sample Output 2:

88

这题主要要弄清楚LL旋转、RR旋转、LR旋转、RL旋转分别是怎么操作，怎么用代码表示：

1、可以看出来，RR旋转是将B的左树连到A的右边，然后B的左树变为A即可，代码为：

Tree single_right_rotation(Tree A)
{
    Tree B=A->right;
    A->right=B->left;
    B->left=A;
    A->height = Max(GetHeight(A->left), GetHeight(A->right))+1;
    B->height = Max(GetHeight(B->left), GetHeight(B->right))+1;
    
    return B;
}

 

2、LL旋转是将B的右子树连到A的左边，B的右子树变为A。代码表示为：

Tree single_left_rotation(Tree A)
{
    Tree B=A->left;
    A->left = B->right;
    B->right=A;
    A->height = Max(GetHeight(A->left), GetHeight(A->right))+1;
    B->height = Max(GetHeight(B->left), GetHeight(B->right))+1;
    
    return B;
}

3、LR旋转看着不太明显，其实可以看成先将B--C这段进行右单旋（图中红色框住的部分），也就是C连上了A，然后B在C的左边；随后，对C----A这段进行左单旋，将C放在了最上面，A在C的右侧。代码实现为：

Tree left_right_rotation(Tree A)
{
    A->left=single_right_rotation(A->left);
    return single_left_rotation(A);
}

 4、RL旋转同理，红色线框中的部分是不是和左单旋非常像。所以先对这部分做左单旋，然后对A----C部分做右单旋。代码实现为：

Tree right_left_rotation(Tree A)
{
    A->right=single_left_rotation(A->right);
    return single_right_rotation(A);
} 

 弄明白了核心原理，接下来就是输出代码了：

这其中有关于左右子树高度的判断代码GetHeight，毕竟想要得到平衡二叉树，首先得知道什么时候不平衡

//04-树5 Root of AVL Tree
#include<stdio.h>
#include<stdlib.h>

struct AVLtree_Node{
    int number;
    struct AVLtree_Node* left;
    struct AVLtree_Node* right;
    int height;
};

typedef struct AVLtree_Node* Tree;

int Max(int a, int b);
int GetHeight(Tree T);
Tree single_left_rotation(Tree A);
Tree single_right_rotation(Tree A);
Tree left_right_rotation(Tree A);
Tree right_left_rotation(Tree A);
Tree NewNode(int Data);
Tree Insert(Tree T, int Data);

int main()
{
    int N=0, i=0, Data=0;
    scanf("%d", &N);
    if(N){
        scanf("%d", &Data);
        Tree T= NewNode(Data);
        for(i=1;i<N;i++){
            scanf("%d", &Data);
            T = Insert(T,Data);
        }
        printf("%d", T->number);
    }
    
    return 0;
}

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

int GetHeight(Tree T)      //关于左右子树高度的判断
{
    int Hl, Hr, MaxH;
    if(T){
        Hl=GetHeight(T->left);
        Hr=GetHeight(T->right);
        MaxH = Max (Hl, Hr);
        return MaxH+1;
    }
    
    else return 0;
}

Tree single_left_rotation(Tree A)
{
    Tree B=A->left;
    A->left = B->right;
    B->right=A;
    A->height = Max(GetHeight(A->left), GetHeight(A->right))+1;
    B->height = Max(GetHeight(B->left), GetHeight(B->right))+1;
    
    return B;
}

Tree single_right_rotation(Tree A)
{
    Tree B=A->right;
    A->right=B->left;
    B->left=A;
    A->height = Max(GetHeight(A->left), GetHeight(A->right))+1;
    B->height = Max(GetHeight(B->left), GetHeight(B->right))+1;
    
    return B;
}

Tree left_right_rotation(Tree A)
{
    A->left=single_right_rotation(A->left);
    return single_left_rotation(A);
}

Tree right_left_rotation(Tree A)
{
    A->right=single_left_rotation(A->right);
    return single_right_rotation(A);
}

Tree NewNode(int Data)
{
    Tree T = (Tree) malloc (sizeof(struct AVLtree_Node)) ;
    T->height=0;
    T->left=T->right=NULL;
    T->number=Data;
    
    return T;
}

Tree Insert(Tree T, int Data)
{
    if(!T) T = NewNode(Data);
    else{
        if(Data>T->number) {
            T->right=Insert(T->right, Data);
            if(GetHeight(T->right)-GetHeight(T->left)==2){   
                if(Data > T->right->number) T=single_right_rotation(T);
                else T=right_left_rotation(T);
            }
        }
        else{
            T->left=Insert(T->left, Data);
            if(GetHeight(T->right)-GetHeight(T->left)==-2){   //平不平衡的判断
                if(Data < T->left->number) T=single_left_rotation(T);
                else T=left_right_rotation(T);
            }
        }
    }
    T->height = Max(GetHeight(T->left), GetHeight(T->right))+1;
    
    return T;
}

 

 

标签：--------,right,04,int,Tree,GetHeight,rotation,left
来源： https://blog.csdn.net/weixin_60245632/article/details/119332349