正确使用remove（）函数？

Question

i'm working on this personal project and i'm a bit confused on how the remove() function works.

header:

class IntSet {

public:

    IntSet(); //Constructor
    ~IntSet(); //Destructor
    int size() ; //
    bool isEmpty();
    bool contains(int number1);
    void add(int number2);
    void remove(int number2);

private:
    int* ptr; //pointer to the array
    int sizeOfArray; //current size of the array
    int currentValue; //number of values currently in IntSet
};

main (only including add() part)

        #include "IntSet.hpp"
    #include <iostream>

    IntSet::IntSet(){

        sizeOfArray = 10;
        currentValue = 0;
        ptr = new int[10];

    }



    IntSet::~IntSet(){
        delete[] ptr;
    }

    //returning the number of values in the IntSet

    int IntSet::size() 
    {
        return currentValue;
    }

    //Determining whether the stack is empty

    bool IntSet::isEmpty()
    {
        if (currentValue == 0)
            return true;
        else
            return false;
    }

    //defining contains() function 

    bool IntSet::contains(int number1)
    {
        for (int i = 0; i < currentValue; i++)
        {
            if (ptr[i] == number1)
                return true;
        }

        return false;
    }

        //defining add() function 

        void IntSet::add(int number2)
        {
            if (currentValue == sizeOfArray)
            {
                sizeOfArray = sizeOfArray * 2; //doubling size of arrayCapacity

                int* temp = new int[sizeOfArray]; //allocating new one that's twice as large

                for (int i = 0; i < currentValue; i++)
                {
                    temp[i] = ptr[i]; //copying old stuff into new one
                }

                delete[] ptr; //deallocate old array
                ptr = temp; //set ptr to new array
            }

        }

    //defining remove() function goes here

So for the add() function I had to take an int parameter add it to the array. When it gets full I have to double the size of the array, copy the contents of the old array into the new one, redirect the data member pointer to the new array and then deallocate the array.

For the remove() function I have to just take an int parameter and remove it from the IntSet by shifting over all the subsequent elements of the array. Should I just use parts of my add function and pretty much tell it to do the opposite for my remove() function? If not, how do I even begin to write the remove() function? I'll show the rest of my code if needed. Thank you guys so much!

Answer 1

Give this a try for removing:

void IntSet::remove(int number2)
{
    bool bIntRemoved = false;
    for(int i=0; i < currentValue; i++){
        // check if we are currently searching or shifting
        if(!bIntRemoved){
            // still searching
            // check if we should remove int at current index
            if(ptr[i] == number2){
                // found the int to remove
                // We'll decrement i and set bIntRemoved = to true
                // So the else-if code handles shifting over the array
                    i--;
                bIntRemoved = true;
            }
        }else if(i < currentValue-1){
            // We have spots to shift
            // Check if this is the last index
            ptr[i] = ptr[i+1];
        } // else, we are at the last index and we have nothing to shift
    }

    if(bIntRemoved){
        // The int was successfully located and any necessary shifting has been
        // executed. Just decrement currentValue so the current last index will be
        // disregarded.
        currentValue--;
    } // else, the int to remove could not be located
}

I haven't tested, but in theory, this should locate the first instance of the int you need to remove, shift all values left by one spot (unless the int to remove is in the last index of the array), and then decrement the currentValue variable so the previous last index of the array is disregarded and can be overwritten. Anyway, sorry if that's a poor explanation, but it's not the easiest concept to explain. I attempted to document the code fairly well, so hopefully that will make sense :P Let me know if you have any questions and let me know if this works or doesn't work for you ( I find feedback to be very important. )

EDIT: Also, I intended to mention this, but I forgot, so thank you, @Viet, for mentioning this in your answer, your add() function does not seem to handle cases when the currentValue is less than the size of the array. I assume you are already handling that and you just omitted the else statement that takes care of it?

EDIT #2: The following is code to properly handle adding new elements to the array:

void IntSet::add(int number2){
    if (currentValue == sizeOfArray)
    {
        sizeOfArray = sizeOfArray * 2; //doubling size of arrayCapacity

        // nothrow is used below to allow for graceful error handling if there is not enough
        // ram to create the new array
        int* temp = new (nothrow) int[sizeOfArray]; //allocating new one that's twice as large

        // check if new int array could be create
        if(temp == nullptr){
            // new int array could not be created
            /** Possibly set an error flag here or in some way warn the calling function that
                the function failed to allocate the necessary memory space.
                I'll leave that up to you, OP. **/

            // Right now we'll just return without modifying the existing array at all
            return;
        }

        for (int i = 0; i < currentValue; i++)
        {
            temp[i] = ptr[i]; //copying old stuff into new one
        }
        delete[] ptr; //deallocate old array
        ptr = temp; //set ptr to new array

        // Now we'll just let the code below add the number to the array

    } // else we have enough space to add the number to the array

    ptr[currentValue] = number2;
    currentValue++;
}

Again, I have not tested this code, but let me know if it works or does not work for you. Also, I modified the line that makes a new array ( int *temp = new int[sizeOfArray]; ) to now handle errors if memory cannot successfully be allocated. To do this I am using the (nothrow) object (more on that on this CPlusPlus page ). If allocation fails, a temp is set to a null pointer. Without this, the method would instead throw a bad_alloc exception or the program would terminate. That's not very graceful, so I prefer properly handling the error (and handling it in a way that is less strenuous on the calling function). To use this, you will need to include the <new> header (which is where nothrow is defined).

Answer 2

Is your class is a set or a list? If your class is a set, it mean there are no same numbers in your class Example: a set {1, 2, 3}, a list: {1, 2, 3, 1, 3, 2}

About your add function, i have some comments:

• You does not check new element exist in your set
• You does not increase current size and set value for new element in your set
• You can use memcpy function to copy old data to new data pointer

About remove function, i have some ideas:

• At first, you must find the position of number which need to be delete in current set
• After that, you remove that number by shift left all member from next position of number which need to be delete to the left position. And you must decrease current size by 1

Example: you have a set {1, 2, 3, 4}, current size is 4. And you want to remove a number "2"

• First, you find the position of 2 in your set. It is 1 (because the start index of array is start from 0)
• Second, you remove it by pushing back all the values from next position on the front of its in your set. Ex: the value of position 1 replaced by value 3, the value of position 2 replaced by value 4
• Finally, you decrease current size by 1. Now, current size is 3, and you have a new set {1, 3, 4}