数据结构与算法分析 3.26 — 双端队列的实现

struct DequeRecord;
typedef struct DequeRecord *Deque;

struct DequeRecord
{
    int Capacity;
    int Left;
    int Right;
    ElementType *Array;
};

Deque CreateDeque( int MaxElements );
int IsEmpty( Deque D );
int IsFull( Deque D );
void MakeEmpty( Deque D );
void Push_Left( ElementType X, Deque D );
void Push_Right( ElementType X, Deque D );
ElementType Pop_Left( Deque D );
ElementType Pop_Right( Deque D );
void DisposeDeque( Deque D );


Deque CreateDeque( int MaxElements )
{
    Deque D;

    D = (Deque)malloc( sizeof(struct DequeRecord) );
    if ( D == NULL )
    {
        printf( "Out of space" );
        return NULL;
    }

    D->Array = (ElementType *)malloc( sizeof(ElementType) * MaxElements );
    if ( D->Array == NULL )
    {
        printf( "Out of space" );
        return NULL;
    }

    D->Capacity = MaxElements;
    MakeEmpty( D );

    return D;
}

int IsEmpty( Deque D )
{
    return D->Left == D->Right;
}

int IsFull( Deque D )
{ 
    return ( D->Left + D->Capacity - 1 ) % D->Capacity == D->Right;
}

void MakeEmpty( Deque D )
{
    D->Left = 0;
    D->Right = 0;
}

void Push_Left( ElementType X, Deque D )
{
    if ( IsFull(D) )
        printf( "Full deque" );
    else
    {
        D->Left = ( D->Left - 1 + D->Capacity ) % D->Capacity;
        D->Array[D->Left] = X;
    }
}

void Push_Right( ElementType X, Deque D )
{
    if ( IsFull(D) )
        printf( "Full deque" );
    else
    {
        D->Array[D->Right] = X;
        D->Right = ( D->Right + 1 ) % D->Capacity;
    }
}

ElementType Pop_Left( Deque D )
{
    ElementType TmpCell;

    if ( IsEmpty(D) )
    {
        printf( "Empty deque" );
        return 0; // 应该返回无效元素
    }
    else
    {
        TmpCell = D->Array[D->Left];
        D->Left = ( D->Left + 1 ) % D->Capacity;
    }

    return TmpCell;
}

ElementType Pop_Right( Deque D )
{
    ElementType TmpCell;

    if ( IsEmpty(D) )
    {
        printf( "Empty Deque" );
        return 0;
    }
    else
    {
        D->Right = ( D->Right - 1 + D->Capacity ) % D->Capacity;
        TmpCell = D->Array[D->Right];
    }

    return TmpCell;
}

void DisposeDeque( Deque D )
{
    if ( D != NULL )
    {
        free( D->Array );
        free( D );
    }
}