6-2 Two Stacks In One Array (20 分)（C source code）

Write routines to implement two stacks using only one array. Your stack routines should not declare an overflow unless every slot in the array is used.

Format of functions:

Stack CreateStack( int MaxElements );
int IsEmpty( Stack S, int Stacknum );
int IsFull( Stack S );
int Push( ElementType X, Stack S, int Stacknum );
ElementType Top_Pop( Stack S, int Stacknum );

where int Stacknum is the index of a stack which is either 1 or 2; int MaxElements is the size of the stack array; and Stack is defined as the following:

typedef struct StackRecord *Stack;
struct StackRecord  {
    int Capacity;       
    int Top1;           
    int Top2;           
    ElementType *Array; 
}

Note: Push is supposed to return 1 if the operation can be done successfully, or 0 if fails. If the stack is empty, Top_Pop must return ERROR which is defined by the judge program.

Sample program of judge:

#include 
#include 
#define ERROR 1e8
typedef int ElementType;
typedef enum { push, pop, end } Operation;

typedef struct StackRecord *Stack;
struct StackRecord  {
    int Capacity;       
    int Top1;           
    int Top2;           
    ElementType *Array; 
};

Stack CreateStack( int MaxElements );
int IsEmpty( Stack S, int Stacknum );
int IsFull( Stack S );
int Push( ElementType X, Stack S, int Stacknum );
ElementType Top_Pop( Stack S, int Stacknum );

Operation GetOp();  
void PrintStack( Stack S, int Stacknum ); 

int main()
{
    int N, Sn, X;
    Stack S;
    int done = 0;

    scanf("%d", &N);
    S = CreateStack(N);
    while ( !done ) {
        switch( GetOp() ) {
        case push: 
            scanf("%d %d", &Sn, &X);
            if (!Push(X, S, Sn)) printf("Stack %d is Full!n", Sn);
            break;
        case pop:
            scanf("%d", &Sn);
            X = Top_Pop(S, Sn);
            if ( X==ERROR ) printf("Stack %d is Empty!n", Sn);
            break;
        case end:
            PrintStack(S, 1);
            PrintStack(S, 2);
            done = 1;
            break;
        }
    }
    return 0;
}

Sample Input:

5
Push 1 1
Pop 2
Push 2 11
Push 1 2
Push 2 12
Pop 1
Push 2 13
Push 2 14
Push 1 3
Pop 2
End

结尾无空行

Sample Output:

Stack 2 is Empty!
Stack 1 is Full!
Pop from Stack 1: 1
Pop from Stack 2: 13 12 11

结尾无空行

思路

 用ppt做了张图~感觉题目还是很好懂哒

就是一个数组存放了两个两个数组，一个从头开始(Stack1每插入一个，Top1++)，一个从尾开始(Stack2每插入一个，Top1--)

我将Top1初始为0，Top2初始为最后一个位置。如下图：

 第二种情况就是存满的情况啦，此时Top1>Top2

答案（AC）

Stack CreateStack( int MaxElements ){
    Stack S=(Stack)malloc(sizeof(struct StackRecord));
    S->Capacity=MaxElements;
    S->Array=(ElementType*)malloc(sizeof(ElementType)*MaxElements);
    S->Top1=0;
    S->Top2=MaxElements-1;
    return S;
}
int IsEmpty( Stack S, int Stacknum ){
    if(Stacknum==1){
        if(S->Top1==0)return 1;
    }else{
        if(S->Top2==S->Capacity-1)return 1;
    }
    return 0;
}
int IsFull( Stack S ){
    if(S->Top1>S->Top2)return 1;
    else return 0;
}
int Push( ElementType X, Stack S, int Stacknum ){
    if(IsFull(S))return 0;
    if(Stacknum==1){
        S->Array[(S->Top1)++]=X;
    }else{
        S->Array[(S->Top2)--]=X;
    }
    return 1;
}
ElementType Top_Pop( Stack S, int Stacknum ){
    if(IsEmpty(S,Stacknum))return ERROR;
    int X;
    if(Stacknum==1){
        X=S->Array[--(S->Top1)];
    }else{
        X=S->Array[++(S->Top2)];
    }
    return X;
}

作业都是用C写的哈（其实是我现在只会C）