3.1.cpp

#include <iostream>
using namespace std;

class stack3{
public:
    stack3(int size = 300){
        buf = new int[size*3];
        ptop[0]=ptop[1]=ptop[2]=-1;
        this->size = size;
    }
    ~stack3(){
        delete[] buf;
    }
    void push(int stackNum, int val){
        int idx = stackNum*size + ptop[stackNum] + 1;
        buf[idx] = val;
        ++ptop[stackNum];
    }
    void pop(int stackNum){
        --ptop[stackNum];
    }
    int top(int stackNum){
        int idx = stackNum*size + ptop[stackNum];
        return buf[idx];
    }
    bool empty(int stackNum){
        return ptop[stackNum]==-1;
    }

private:
    int *buf;
    int ptop[3];
    int size;
};

typedef struct node{
    int val,preIdx;
}node;

class stack3_1{
public:
    stack3_1(int totalSize = 900){
        buf = new node[totalSize];
        ptop[0]=ptop[1]=ptop[2]=-1;
        this->totalSize = totalSize;
        cur = 0;
    }
    ~stack3_1(){
        delete[] buf;
    }
    void push(int stackNum, int val){
        buf[cur].val = val;
        buf[cur].preIdx = ptop[stackNum];
        ptop[stackNum] = cur;
        ++cur;
    }
    void pop(int stackNum){
        ptop[stackNum] = buf[ptop[stackNum]].preIdx;
    }
    int top(int stackNum){
        return buf[ptop[stackNum]].val;
    }
    bool empty(int stackNum){
        return ptop[stackNum]==-1;
    }

private:
    node *buf;
    int ptop[3];
    int totalSize;
    int cur;
};

int main(){
    stack3_1 mystack;//stack3 mystack;
    for(int i=0; i<10; ++i)
        mystack.push(0, i);
    for(int i=10; i<20; ++i)
        mystack.push(1, i);
    for(int i=100; i<110; ++i)
        mystack.push(2, i);
    for(int i=0; i<3; ++i)
        cout<<mystack.top(i)<<" ";

    cout<<endl;
    for(int i=0; i<3; ++i){
        mystack.pop(i);
        cout<<mystack.top(i)<<" ";
    }
    mystack.push(0, 111);
    mystack.push(1, 222);
    mystack.push(2, 333);
    for(int i=0; i<3; ++i)
        cout<<mystack.top(i)<<" ";
    return 0;
}