p74e5

stack.h

#include <iostream>
#include <cstdlib>

class Stack {
private:
    int* _stack;
    int _size;
public:
    Stack() {
        this->_size = 0;
        this->_stack = (int *)malloc(0);
        }
    ~Stack() { this->empty(); }
    void push(int item);

    int peek();
    int pop();
    int getSize();

    void empty();
private:
    void _extend();
    void _shrink();
    void _allocate();
};
------------------------

stack.cpp

#include "Stack.h"

void Stack::push(int item) {
   this->_extend();
   this->_stack[this->_size-1] = item;
}

int Stack::peek() {
    return this->_stack[this->_size-1];
}

int Stack::pop() {
    int item = this->_stack[this->_size-1];
    this->_shrink();
    return item;
}

int Stack::getSize() {
    return this->_size;
}

void Stack::empty() {
    while (this->_size) this->_shrink();
}

void Stack::_extend() {
    this->_size++;
    this->_allocate();
}

void Stack::_shrink() {
    this->_size--;
    this->_allocate();
}

void Stack::_allocate() {
    this->_stack = (int *)realloc(this->_stack,
                                  this->_size * sizeof(int));
}

---------
main.cpp

#include "Stack.h"
#include <cstdio>
using namespace std;

int main(void) {
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
    int size, x, y, tmp;
    cin >> size >> x >> y;

    Stack* s = new Stack();

    for (int i = 0; i < size; i++) {
        cin >> tmp;
        s->push(tmp);
    }

    Stack *result = new Stack();
    while(s->getSize()) {
        int item = s->pop();
        if (item == x) {
            result->push(y);
        }
        result->push(item);
    }
    while(result->getSize()) {
        cout << result->pop() << " ";
    }
    cout << endl;
}