CareerCup-3.1

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Describe how you could use a single array to implement three stacks

Approach 1:

#include <iostream>using namespace std;#define SIZE 60#define PERSIZE SIZE/3typedef int Data;class Stack{public:    Stack(int type):mType(type)    {        if(type < 0 || type > 2)        {            throw "Error Stack Type";        } else {            tag = mType * PERSIZE - 1;        }    };    void push(Data d)    {        if(tag >= (mType + 1) * PERSIZE - 1)        {            throw "Out of Size";        } else {            data[++tag] = d;        }    };    void pop()    {        if(tag < mType * PERSIZE)        {            throw "Empty Stack";        } else {            tag --;        }    };    Data peek()    {        if(tag < mType * PERSIZE)        {            throw "Empty Stack";        } else {            return data[tag];        }    };    bool isEmpty(){return tag >= mType * PERSIZE;};private:    static Data data[SIZE];    int mType;    int tag;};Data Stack::data[SIZE];

Approach 2:

#include <iostream>using namespace std;#define SIZE 60typedef int Data;struct Node  {    Data data;      int next;  };class Stack{public:    Stack(int type):mType(type)    {        if(type < 0 || type > 2)        {            throw "Error Stack Type";        }    };    void push(Data d)    {        if(tag >= SIZE-1)        {            throw "Stack Full";        }        data[++tag].data = d;        if(top[mType] < 0)            data[tag].next = -1;        else            data[tag].next = top[mType];        top[mType] = tag;    };    void pop()    {        if(top[mType] < 0)        {            throw "Empty Stack";        }        top[mType] = data[top[mType]].next;        tag--;    };    Data peek()    {        if(top[mType] < 0)        {            throw "Empty Stack";        } else {            return data[top[mType]].data;        }    };    bool isEmpty(){return top[mType] >= 0;};private:    static Node data[SIZE];    int mType;    static int top[3];    static int tag;};Node Stack::data[SIZE];int Stack::tag = -1;int Stack::top[3] = {-1, -1, -1};