Two Stacks In One Array

6-1 Two Stacks In One Array （20 分）

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;       /* maximum size of the stack array */
    int Top1;           /* top pointer for Stack 1 */
    int Top2;           /* top pointer for Stack 2 */
    ElementType *Array; /* space for the two stacks */
}

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 ERRORwhich is defined by the judge program.

Sample program of judge:

#include <stdio.h>
#include <stdlib.h>
#define ERROR 1e8
typedef int ElementType;
typedef enum { push, pop, end } Operation;

typedef struct StackRecord *Stack;
struct StackRecord  {
    int Capacity;       /* maximum size of the stack array */
    int Top1;           /* top pointer for Stack 1 */
    int Top2;           /* top pointer for Stack 2 */
    ElementType *Array; /* space for the two stacks */
};

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();  /* details omitted */
void PrintStack( Stack S, int Stacknum ); /* details omitted */

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;
}

/* Your function will be put here */

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

Sample Output:

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

作者: 陳越

單位: 浙江大學

時間限制: 400 ms

內存限制: 64 MB

代碼長度限制: 16 KB

 

#include <stdio.h>
#include <stdlib.h>
#define ERROR 1e8
typedef int ElementType;
typedef enum { push, pop, end } Operation;

typedef struct StackRecord *Stack;
struct StackRecord {
	int Capacity;       /* maximum size of the stack array */
	int Top1;           /* top pointer for Stack 1 */
	int Top2;           /* top pointer for Stack 2 */
	ElementType *Array; /* space for the two stacks */
};

Stack CreateStack(int MaxElements)
{
	Stack s = (Stack)malloc(sizeof(struct StackRecord));
	s->Capacity = MaxElements;
	s->Top1 =-1;
	s->Top2 = MaxElements;
	s->Array=(int)malloc(sizeof(int)*MaxElements);
	return s;
	//在C語言中Array的下標從0到MaxElements-1，Top1和Top2分別從兩頭向中間標記
}
int IsEmpty(Stack S, int Stacknum)
{
	//當Top1和Top2等於CreateStack中賦予的原值時，返回1
	if (Stacknum == 1) {
		if (S->Top1 == -1)return 1;
		else return 0;
	}
	else if (Stacknum == 2) {
		if (S->Top2 == S->Capacity)return 1;
		else return 0;
	}
}
int IsFull(Stack S)
{
	//當Top1和Top2相差僅剩1時，Capacity已用完，棧滿
	if (S->Top2-S->Top1==1)return 1;
	return 0;
}
int Push(ElementType X, Stack S, int Stacknum)
{
	//先將指針指向下一位置，再將X值賦予該位置的指針
	if (IsFull(S))return 0;
	if (Stacknum == 1)
		S->Array[++(S->Top1)] = X;
	else if (Stacknum == 2) 
		S->Array[--(S->Top2)] = X;

	return 1;
}
ElementType Top_Pop(Stack S, int Stacknum)
{
	//先將此處指針的值返回，再將指針移向上一位置
	if (IsEmpty(S, Stacknum))return ERROR;
	if (Stacknum == 1) {
		return S->Array[(S->Top1)--];
	}
	else if (Stacknum == 2) {
		return S->Array[(S->Top2)++];
	}
}

Operation GetOp()
{
	char s[100];
	scanf("%s", s);
	if (!strcmp(s, "Push")) return push;
	if (!strcmp(s, "Pop")) return pop;
	if (!strcmp(s, "End")) return end;

}
void PrintStack(Stack S, int Stacknum)
{
	printf("Pop from Stack %d:", Stacknum);
	while (!IsEmpty(S, Stacknum))
	{
		printf("%d ", Top_Pop(S, Stacknum));
	}
	puts("");
}

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;
}