This practice problem will require you to implement a simple list, supporting some common functions.

The expected header is as follows (p025.h):

#ifndef _P025
#define _P025
class MyList {
    int value;
    MyList* next;
    MyList* last;
public:
    int length;

    MyList();
    ~MyList();
    void prepend(int val);
    void append(int val);
    int get(int ind);
    int give(int ind, int val);
};
#endif

Class Specification

MyList::MyList

Constructor. This should initialise the value of value to -1, and next and last to NULL (or 0x0).

void MyList::prepend(int val);

Insert val to the beginning of the list.

void append(int val);

Insert val to the end of the list.

int get(int ind);

Return the value at index ind. If ind is out of bound, you should return -1.

int give(int ind, int val);

Change the value at index ind to val, and return val. If ind is out of bound, you should return -1.

Testing

Main programme (main.cpp):

#include <iostream>
#include "p025.h"
using namespace std;

int main() {
    int n, k, val;
    cin >> n;
    MyList list;
    for (int i=0;i<n;i++) {
        cin >> k >> val;
        if (k==0){
            list.prepend(val);
        } else if (k==1) {
            list.append(val);
        } else if (k==2) {
            cout << list.get(val) << endl;
        } else {
            int op;
            cin >> op;
            cout << list.give(val, op) << endl;
        }
    }
    return 0;
}

You can use this programme to run some tests. The main programme is expecting a single number n on the first line.

The following n lines each contain integers k, val, and optionally op, calling the class to perform specific actions.

Sample Input

5
0 1
0 2
2 -1
2 0
2 1

Sample Output

-1
2
1