c++ - 编写 bool 表达式来判断列表是否在增加

Question

我有下面给出的程序，我能够完成对某个点的分配，除了添加一个菜单选项，如果给定列表增加或减少，则返回 true/false例如，对于包含 head-() (11) (8) (15) (3) 的列表，isIncreasing() 应该返回 false。但是，在处理包含 head- () (7) (9) (15) 的列表时，它将返回 true。

我如何查看列表并告诉程序比较值并做出决定

赋值告诉我们这个新操作应该有签名:

bool 列表::isIncreasing() 常量;

列表.H

#ifndef LIST_H
#define LIST_H
#include <iostream>
#include "ListNode.h"
#include "ListIterator.h"

namespace cs20 {

template <class Object>
class List {
public:
    List();
    List( const List& rhs );
    ~List();

    bool isEmpty() const;
    void makeEmpty();
    ListIterator<Object> zeroth() const;
    ListIterator<Object> first() const;
    void insert( const Object& data,
                 const ListIterator<Object> &iter );
    void insert( const Object& data );
    ListIterator<Object> findPrevious( const Object& data ) const;
    void remove( const Object& data );

    const List& operator =( const List& rhs );
private:
    ListNode<Object> * head;

};

}
#endif

列表.CPP

#ifndef LIST_CPP
#define LIST_CPP

#include "List.h"

namespace cs20 {
template <class Object>
List<Object>::List() {
    head = new ListNode<Object>;
}

template <class Object>
List<Object>::List( const List<Object>& rhs ) {
    head = new ListNode<Object>;
    *this = rhs;
}

template <class Object>
List<Object>::~List() {
    makeEmpty();
    delete head;
}

template <class Object>
bool List<Object>::isEmpty() const {
    return( head->nextIsNull() );
}

template <class Object>
void List<Object>::makeEmpty() {
    while (!isEmpty()) {
        remove( first().retrieve() );
    }
}

template <class Object>
ListIterator<Object> List<Object>::zeroth() const {
    return( ListIterator<Object>( head ) );
}

template <class Object>
ListIterator<Object> List<Object>::first() const {
    return( ListIterator<Object>( head->getNext() ) );
}

template <class Object>
void List<Object>::insert( const Object& data,
                           const ListIterator<Object> &iter ) {
    if (iter.isValid()) {
        ListNode<Object>* newnode = new ListNode<Object>( data, iter.current->getNext() );
        iter.current->setNext( newnode );
    }
}

template <class Object>
void List<Object>::insert( const Object& data ) {
    // insert after the header node
    ListNode<Object>* newnode = new ListNode<Object>( data, head->getNext() );
    head->setNext( newnode );
}

template <class Object>
ListIterator<Object> List<Object>::findPrevious( const Object& data ) const {
    ListNode<Object>* node = head;
    while( node->getNext() != NULL && node->getNext()->getElement() != data ) {
        node = node->getNext();
    }
    if (node->getNext() == NULL) {
        node = NULL;
    }
    return ListIterator<Object>( node );
}

template <class Object>
void List<Object>::remove( const Object& data ) {
    ListIterator<Object> iter = findPrevious( data );
    if (iter.isValid()) {
        ListNode<Object>* node = findPrevious( data ).current;
        if (node->getNext() != NULL) {
            ListNode<Object> *oldNode = node->getNext();
            node->setNext( node->getNext()->getNext() );  // Skip oldNode
            delete oldNode;
        }
    }
}

// Deep copy of linked list
template <class Object>
const List<Object>& List<Object>::operator =( const List<Object>& rhs ) {
    if (this != &rhs) {
        makeEmpty();

        ListIterator<Object> rightiter = rhs.first( );
        ListIterator<Object> myiterator = zeroth();
        while( rightiter.isValid() ) {
            insert( rightiter.retrieve(), myiterator );
            rightiter.advance();
            myiterator.advance();
        }
    }
    return( *this );
}

}

#endif

实现列表菜单.CPP

//Menu.cpp : 定义控制台应用程序的入口点。//

#include <iostream>
#include "List.h"
#include "ListNode.h"
#include "ListIterator.h"
#include "List.cpp"
#include "ListNode.cpp"
#include "ListIterator.cpp"

using namespace std;
using namespace cs20;

enum CHOICE {MAKEEMPTY, REMOVE, ISEMPTY, FINDPREVIOUS, INSERT, QUIT, PRINT };

CHOICE menu();
void printList( const List<int>& l );

int main(int argc, char* argv[]) {
    int value;
    List<int> list;
    ListIterator<int> iter;

    CHOICE choice;
    do {
        choice = menu();
        switch( choice ) {
        case MAKEEMPTY:
            list.makeEmpty();
            break;
        case ISEMPTY:
            if (list.isEmpty()) {
                cout << "list is empty" << endl;
            }
            else {
                cout << "list is not empty" << endl;
            }
            break;
        case REMOVE:
            cout << "Please provide int to remove: ";
            cin  >> value; 
            list.remove( value );
            break;
        case INSERT:
            cout << "Please provide int to insert: ";
            cin  >> value; 
            list.insert( value );
            break;
        case FINDPREVIOUS:
            cout << "Please provide int to find: ";
            cin  >> value; 
            iter = list.findPrevious( value );
            if (iter.isValid()) {
                cout << "previous element = " << iter.retrieve() << endl;
            }
            else {
                cout << "data element was not found!" << endl;
            }
            break;
        case PRINT:
            printList( list );
            break;
        case QUIT:
            break;
    }   

    } while (choice != QUIT);

    return( 0 );
}

int sample() {
    cout << "Forming Lists" << endl;
    int one = 1, two = 2;
    List<int> l1 = List<int>();
    List<int> l2 = List<int>();

    l1.insert( one );
    l1.insert( two );

    cout << "print l1" << endl;
    printList( l1 );

    cout << "l2 = l1" << endl;
    l2 = l1;

    cout << "print l2" << endl;
    printList( l2 );    

    cout << "l1.remove(one)" << endl;
    l1.remove( one );

    cout << "print l1" << endl;
    printList( l1 );

    cout << "print l2" << endl;
    printList( l2 );
    cout << "findPrevious 1 in l2" << endl;
    ListIterator<int> iter = l2.findPrevious( one );
    if (iter.isValid()) {
        cout << "--iter valid" << endl;
        cout << iter.retrieve() << endl;
    }
    else {
        cout << "--iter not valid" << endl;
    }

    cout << "findPrevious 2 in l2" << endl;
    iter = l2.findPrevious( two );
    if (iter.isValid()) {
        cout << "--iter valid" << endl;
        cout << iter.retrieve() << endl;
    }
    else {
        cout << "--iter not valid" << endl;
    }

    cout << "findPrevious 1 in l1" << endl;
    iter = l1.findPrevious( one );
    if (iter.isValid()) {
        cout << "--iter valid" << endl;
        cout << iter.retrieve() << endl;
    }
    else {
        cout << "--iter not valid" << endl;
    }

    cout << "findPrevious 2 in l1" << endl;
    iter = l1.findPrevious( two );
    if (iter.isValid()) {
        cout << "--iter valid" << endl;
        cout << iter.retrieve() << endl;
    }
    else {
        cout << "--iter not valid" << endl;
    }

    cout << "print l1" << endl;
    printList( l1 );    

        // you can remove whatever you want, whether it exists or not
    cout << "l1.remove(one)" << endl;
    l1.remove( one );

    cout << "print l1" << endl;
    printList( l1 );    

    return( 0 );
}

void printList( const List<int>& l ) {
    if (l.isEmpty())
        cout << "Empty list" << endl;
    else {
        ListIterator<int> iter = l.first();
        while (iter.isValid()) {
            cout << iter.retrieve() << " -> ";
            iter.advance();
        }
        cout << "NULL";
        cout << endl;
    }
}

CHOICE menu() {
    char choice;
    CHOICE result;
    cout << "(M)akeEmpty I(s)Empty (R)emove (I)nsert (F)indPrevious (P)rint (Q)uit: " << endl;
    cin  >> choice;
    switch( choice ) {
    case 'M':
    case 'm':
        result = MAKEEMPTY;
        break;
    case 'S':
    case 's':
        result = ISEMPTY;
        break;
    case 'R':
    case 'r':
        result = REMOVE;
        break;
    case 'I':
    case 'i':
        result = INSERT;
        break;
    case 'F':
    case 'f':
        result = FINDPREVIOUS;
        break;
    case 'Q':
    case 'q':
        result = QUIT;
        break;
    case 'P':
    case 'p':
        result = PRINT;
        break;
    }

    return( result );
}

Answer 1

从第一个链接开始:

1. 记录当前链接的值

2. 迭代到下一个链接

3. 测试是否大于(或等于)上一个链接的记录值

4. 如果是，从1开始重复。

5. 否则返回false

如果您一直浏览列表，您就会知道列表一直在递增。