算法（6） —— AVL树

AVL树二叉查找树的一种，所以其操作和二叉查找树的很多操作是相同的。

1. 

#ifndef AVLTREE_H
#define AVLTREE_H

struct AvlNode;
typedef struct AvlNode *Position;
typedef struct AvlNode *AvlTree;

typedef int ElementType;


AvlTree MakeEmpty( AvlTree T );
Position Find( ElementType X, AvlTree T );
Position FindMin( AvlTree T );
Position FindMax( AvlTree T );
AvlTree Insert( ElementType X, AvlTree T );
AvlTree Delete( ElementType X, AvlTree T );
ElementType Retrieve( Position P );

#endif 

2.

#include "avltree.h"
#include <stdlib.h>
#include "fatal.h"

struct AvlNode  {
    ElementType Element;
    AvlTree  Left;
    AvlTree  Right;
    int      Height;
};

AvlTree  MakeEmpty( AvlTree T )   {
    if( T != NULL )
    {
        MakeEmpty( T->Left );
        MakeEmpty( T->Right );
        free( T );
    }
    return NULL;
}

Position  Find( ElementType X, AvlTree T )  {
    if( T == NULL )
        return NULL;
    if( X < T->Element )
        return Find( X, T->Left );
    else if( X > T->Element )
        return Find( X, T->Right );
    else
        return T;
}

Position  FindMin( AvlTree T )  {
    if( T == NULL )
        return NULL;
    else if( T->Left == NULL )
        return T;
    else return FindMin( T->Left );
}

Position  FindMax( AvlTree T )  {
    if( T != NULL )
        while( T->Right != NULL )
            T = T->Right;

    return T;
}

/* START: fig4_36.txt */
static int  Height( Position P )  {
    if( P == NULL )
        return -1;
    else
        return P->Height;
}
/* END */

static int  Max( int Lhs, int Rhs )  {
    return Lhs > Rhs ? Lhs : Rhs;
}

/* START: fig4_39.txt */
/* This function can be called only if K2 has a left child K1 */
/* Perform a rotate between a node (K2) and its left child */
/* Update heights, then return new root k1*/

static Position
SingleRotateWithLeft( Position K2 )  {
    Position K1;

    K1 = K2->Left;
    K2->Left = K1->Right;
    K1->Right = K2;

    K2->Height = Max( Height( K2->Left ), Height( K2->Right ) ) + 1;
    K1->Height = Max( Height( K1->Left ), K2->Height ) + 1;

    return K1;  /* New root */
}
/* END */

/* This function can be called only if K1 has a right child */
/* Perform a rotate between a node (K1) and its right child */
/* Update heights, then return new root */

static Position  SingleRotateWithRight( Position K1 )  {
    Position K2;

    K2 = K1->Right;
    K1->Right = K2->Left;
    K2->Left = K1;

    K1->Height = Max( Height( K1->Left ), Height( K1->Right ) ) + 1;
    K2->Height = Max( Height( K2->Right ), K1->Height ) + 1;

    return K2;  /* New root */
}

/* START: fig4_41.txt */
/* This function can be called only if K3 has a left */
/* child and K3's left child has a right child */
/* Do the left-right double rotation */
/* Update heights, then return new root */

static Position  DoubleRotateWithLeft( Position K3 )   {
    /* Rotate between K1 and K2 */
    K3->Left = SingleRotateWithRight( K3->Left );

    /* Rotate between K3 and K2 */
    return SingleRotateWithLeft( K3 );
}
/* END */

/* This function can be called only if K1 has a right */
/* child and K1's right child has a left child */
/* Do the right-left double rotation */
/* Update heights, then return new root */

static Position  DoubleRotateWithRight( Position K1 )    {
    /* Rotate between K3 and K2 */
    K1->Right = SingleRotateWithLeft( K1->Right );

    /* Rotate between K1 and K2 */
    return SingleRotateWithRight( K1 );
}


AvlTree  Insert( ElementType X, AvlTree T )  {
    if( T == NULL )  {
        T = malloc( sizeof( struct AvlNode ) );
        if( T == NULL )
            FatalError( "Out of space!!!" );
        else     {
            T->Element = X; T->Height = 0;
            T->Left = T->Right = NULL;
        }
    }
    else  if(X < T->Element )  {
        T->Left = Insert( X, T->Left );
        if( Height( T->Left ) - Height( T->Right ) == 2 )
            if( X < T->Left->Element )
                T = SingleRotateWithLeft( T );
            else
                T = DoubleRotateWithLeft( T );
    }
    else  if( X > T->Element )    {
        T->Right = Insert( X, T->Right );
        if( Height( T->Right ) - Height( T->Left ) == 2 )
            if( X > T->Right->Element )
                T = SingleRotateWithRight( T );
            else
                T = DoubleRotateWithRight( T );
    }
    T->Height = Max( Height( T->Left ), Height( T->Right ) ) + 1;
    return T;
}

AvlTree    Delete( ElementType X, AvlTree T )  {
    printf( "Sorry; Delete is unimplemented; %d remains\n", X );
    return T;
}

ElementType Retrieve( Position P )  {
    return P->Element;
}

3.

#include "avltree.c"
#include <stdio.h>

void PrintTree( AvlTree T)  {
    if (T != NULL) {
        PrintTree (T -> Left);
    printf    ("%d\n",Retrieve (T));
        PrintTree (T -> Right);
    }
}


int main(int argc, char *argv[])  {
    AvlTree T;
    Position P;
    int i;
    int j = 0;

    T = MakeEmpty( NULL );
    for( i = 0; i < 50; i += 5 )
        T = Insert( i, T );
    /*for( i = 0; i < 50; i++ )*/
        /*if( ( P = Find( i, T ) ) == NULL || Retrieve( P ) != i )*/
           /*printf( "Error at %d\n", i );*/

 /* for( i = 0; i < 50; i += 2 )
        T = Delete( i, T );

    for( i = 1; i < 50; i += 2 )
        if( ( P = Find( i, T ) ) == NULL || Retrieve( P ) != i )
            printf( "Error at %d\n", i );
    for( i = 0; i < 50; i += 2 )
        if( ( P = Find( i, T ) ) != NULL )
            printf( "Error at %d\n", i );
*/
        PrintTree (T);

    printf( "Min is %d, Max is %d\n", Retrieve( FindMin( T ) ),
               Retrieve( FindMax( T ) ) );

    return 0;
}