[sjtu oj]4370 Min Stack

使用两个栈进行维护

st中存储初始栈内容，并记录节点编号

minn栈中记录各个编号对应的最小值（通过继承上一个与当前值比较实现）

如何实现操作为O（1）：在push&pop的同时维护minn栈

 

代码如下

#include<iostream>
#include<cstring>
#define ll long long
using namespace std;
const ll MAXN=1e6+5;
ll minn[MAXN];

class Stack
{
    private:
        struct Node
        {
            ll data;ll num;
            Node* nex;
            Node(const ll s,Node *nexx=NULL):data(s),nex(nexx){}
            Node():nex(NULL){}
        };
        Node* Top;
        int cnt=0;
    public:
        Stack(){Top=new Node;};
        void pop();
        ll top()const;
        void push(ll s);
        ll getmin();
        ~Stack();
};

Stack a,b;

void Stack::pop()
{
    if(Top->nex==NULL)
    {
        puts("Empty");
        return ;
    }
    cnt--;
    Node* p=Top->nex;
    Top->nex=p->nex;
    delete p;
}

ll Stack::top()const
{
    if(Top->nex==NULL)
    {
        puts("Empty");
        return -1;
    }
    return Top->nex->data;
}

void Stack::push(ll s)
{
    Node *p=new Node;
    p->data=s;
    p->num=++cnt;
    if(Top->nex!=NULL)
    minn[cnt]=min(minn[Top->nex->num],s);
    else minn[cnt]=s;
    p->nex=Top->nex;
    Top->nex=p;
}

ll Stack::getmin()
{
    if(Top->nex==NULL)
    {
        puts("Empty");
        return -1;
    }
    return minn[Top->nex->num];
}

Stack::~Stack()
{
    Node *p=Top;
    while(p)
    {
        Node *q=p->nex;
        delete p;
        p=q;
    }
}

void read(ll &p)
{
    char s=getchar();p=0;
    while(!isdigit(s)) s=getchar();
    for(;isdigit(s);s=getchar()) p=p*10+s-'0';
}

void print(ll p)
{
    if(p/10) print(p/10);
    putchar(p%10+'0');
}

int main()
{
    //memset(minn,0x3f,sizeof(minn));
    ll n,k;
    ll s;
    Stack st;
    read(n);
    for(ll i=1;i<=n;i++)
    {
        read(k);++k;
        ll tem;
        switch(k)
        {
            case 1:read(s);
                   st.push(s);
                   break;
            case 2:st.pop();
                   break;
            case 3:tem=st.top();if(tem!=-1) {print(tem);puts("");}
                   break;
            case 4:tem=st.getmin();
                   if(tem!=-1) {print(tem);puts("");}
                   break;
        }
    }
    
    return 0;
}