面试金典--一个数组实现三个栈（固定大小）

#include <iostream>
#include <queue>
#include <climits>
#include <algorithm>
#include <memory.h>
#include <stdio.h>
#include <ostream>
#include <vector>
#include <list>
#include <cmath>
#include <string>
#include <stdexcept>
using namespace std;

class stack3parts
{
    const int stackSize;
    int top1;
    int top2;
    int top3;
    int* data;
public:
    stack3parts(int paramSize):stackSize(paramSize),top1(0),top2(paramSize),top3(2*paramSize)
    {
        data = new int[paramSize*3];
    }

    void push(int stackNum,const int &elem)
    {
        switch(stackNum)
        {
        case 1:
            if(top1 == stackSize)
                throw std::out_of_range("stack1 is full!");
            data[top1++] = elem;
            break;
        case 2:
            if(top2 == 2*stackSize)
                throw std::out_of_range("stack2 is full!");
            data[top2++] = elem;
            break;
        case 3:
            if(top3 == 3*stackSize)
                throw std::out_of_range("stack3 is full!");
            data[top3++] = elem;
            break;
        }
    }

    int pop(int stackNum)
    {
        switch(stackNum)
        {
        case 1:
            if(top1 == 0)
                throw std::out_of_range("stack1 is empty!");
            top1--;
            return data[top1];
            break;
        case 2:
            if(top2 == stackSize)
                throw std::out_of_range("stack2 is empty!");
            top2--;
            return data[top2];
            break;
        case 3:
            if(top3 == 2*stackSize)
                throw std::out_of_range("stack3 is empty!");
            top3--;
            return data[top3];
            break;
        }
    }
};
int main()
{
    stack3parts s(3);
    s.push(1,2);
    s.push(2,3);
    s.push(3,4);

    cout<<s.pop(1)<<endl;
    cout<<s.pop(2)<<endl;
    cout<<s.pop(3)<<endl;

    s.pop(1);
    return 0;
}

这个思路是对一个数组进行固定的大小分配，这样缺点是资源得不到充分利用