栈的基本算法

一、简单介绍
栈是限定进在表尾插入或删除操作的线性表。因此，对栈来说，表尾端有其特殊的含义，成为栈顶(top)，相应地，表头端称为栈底(bottom)。

不含元素的空表称为空栈。栈的修改是按照后进先出的原则进行的，因此，栈又称为后进先出的线性表。

二、栈示意图

三、基本操作

1、栈的初始化: InitStack(&S)
2、栈顶元素插入: Push(&S, &e)
3、栈顶元素获取: GetTop(&S, &e)
4、栈顶元素删除: Pop(&S, &e)
5、栈的长度: StackLength(S)
6、栈的判空: StackEmpty(S)
7、栈元素的访问： StackTraverse(S, visit())
8、栈的清空： ClearStack(&S)
9、栈的销毁： DestroyStack(&S)

四、栈顺序存储的实现

//---------- 栈的顺序存储表示 ---------
#define STACK_INIT_SIZE 100; //存储空间初始分配量
#define STACKINCREMENT  10;  //存储空间分配增量
typedef struct {
    SElemType *base; //在栈构造之前和销毁之后，base的值为NULL
    SElemType *top;  //栈顶指针
    int stacksize;   //当前已分配的存储空间，以元素为单位 
}SqStack;

//---------- 基本操作的函数原型声明 --------
Status InitStack(SqStack &S);    //构造一个空栈S
Status DestroyStack(SqStack &S); //销毁栈S，S不再存在
Status ClearStack(SqStack &S);   //把S置为空栈
Status StackEmpty(SqStack &S);   //若栈S为空栈，则返回TRUE，否则返回FALSE
int StackLength(SqStack &S);     //返回S的元素个数，即栈的长度
Status GetTop(SqStack &S, SElemType &e); //若栈S不空，则用e返回S的栈顶元素，并返回OK，否则返回ERROR
Status Push(SqStack &S, SElemType &e);   //插入元素e为新的栈顶元素
Status Pop(SqStack &S, SElemType &e);    //若栈S不空，则删除S的栈顶元素e，用e返回其值，返回OK，否则返回ERROR
Status StackTraverse(S, visit(SElemType e));        //从栈顶到栈顶依次对每一个元素调用函数visit()。一旦visit()失败，则操作失败

//---------- 基本操作的算法描述 --------
Status InitStack(SqStack &S){
    S.base = (SElemType *)malloc(STACK_INIT_SIZE * sizeof(SElemType))
    if(!S.base) exit(OVERFLOW); //存储分配失败
    S.top = S.base;
    S.stacksize = STACK_INIT_SIZE;
    return OK;
}

Status DestroyStack(SqStack &S){
    free(S.base);
    S.base = NULL;
    S.top = NULL;
    S.stacksize = 0;
    return OK;
}

Status ClearStack(SqStack &S){
    S.top = S.base;
    return OK;
}

Status StackEmpty(SqStack &S){
    if(S.top == S.base) return TRUE;
    return FALSE;
}

int StackLength(SqStack &S){
    return S.top - S.base;
}

Status GetTop(SqStack &S, SElemType &e){
    if(S.top == S.base) return ERROR;
    e = *(S.top - 1);
    return OK;
}

Status Push(SqStack &S, SElemType &e){
    if(S.top - S.base >= S.stacksize){  //栈满，追加存储空间
        S.base = (SElemType *)realloc(S.base, (S.stacksize + STACKINCREMENT) * sizeof(SElemType));
        if(!S.base) exit(OVERFLOW); //存储分配失败
        S.top = S.base + S.stacksize;
        S.stacksize += STACKINCREMENT;
    }
    * S.top++ = e;
    return OK;
}

Status Pop(SqStack &S, SElemType &e){
    if(S.top == S.base) return ERROR;
    e = * --S.top;
    return OK;
}

Status StackTraverse(S, visit()){
    SElemType *base2 = S.base;
    while(S.top > S.base2)
        visit(*S.base2++);
    return OK;
}
Status visit(SElemType e)
{
    printf("%d ", e);
    return OK;
}

五、代码实现

//
//  main.c
//  EEs
//
//  Created by 夏远全 on 2019/9/1.
//  Copyright © 2019 北京一米蓝科技有限公司. All rights reserved.
//

#include <stdio.h>
#include <stdlib.h>
#include <sys/malloc.h>
#include <string.h>
#include <stdio.h>

#define STACK_OVERFLOW   -1
#define STACK_INIT_SIZE 100
#define STACKINCREMENT   10
#define OK               1
#define ERROR            0
#define TRUE             1
#define FALSE            0

typedef int SElemType;
typedef int status;

typedef struct sqstack
{
    SElemType *base;
    SElemType *top;
    int stacksize;
}SqStack;

status Initstack(SqStack *s);
status Destorystack(SqStack *s);
status Clearstack(SqStack *s);
status StackEmpty(SqStack *s);
int StackLength(SqStack *s);
status GetTop(SqStack *s, SElemType *e);
status Push(SqStack *s, SElemType *e);
status Pop(SqStack *s, SElemType *e);
status StackTraverse(SqStack *s, status(*visit)(SElemType e));
status visit(SElemType e);

int main(int argc, const char * argv[]) {

    SElemType i;
    SElemType e = 0;
    SqStack s;
    if(Initstack(&s) == OK){
        for(i = 1; i <= 20; i++){
            Push(&s,&i);
        }
    }
    
    printf("栈中的元素依次为：");
    StackTraverse(&s,visit);
    
    Pop(&s, &e);
    
    GetTop(&s, &e);
    
    StackEmpty(&s);
    
    StackLength(&s);
    
    Clearstack(&s);
    
    StackEmpty(&s);
    
    Destorystack(&s);

    return 0;
}

status Initstack(SqStack *s)
{
    s->base = (SElemType *)malloc(STACK_INIT_SIZE*sizeof(SElemType));
    if(!s->base) return STACK_OVERFLOW;
    s->top = s->base;
    s->stacksize = STACK_INIT_SIZE;
    return OK;
}

status Push(SqStack *s, SElemType *e)
{
    if (s->top - s->base >= s->stacksize) {  //栈满 ，追加空间
        s->base = (SElemType *)realloc(s->base, (s->stacksize + STACKINCREMENT) * sizeof(SElemType));
        if (!s->base) exit(0);
        s->top = s->base + s->stacksize;  // 设置栈顶
        s->stacksize = s->stacksize + STACKINCREMENT;  // 设置栈的最大容量
    }
    *(s->top) = *e;
    s->top ++;
    return OK;
}

status Pop(SqStack *s, SElemType *e)
{
    if(&s->top == &s->base) return ERROR;
    s->top --;
    *e = *(s->top);
    printf("弹出的栈顶元素 e=%d
", *e);
    return OK;
}

status StackTraverse(SqStack *s, status(*visit)(SElemType e))
{
    SElemType *base2 = s->base;
    while(s->top > base2){
        visit(*(base2++));
    }
    printf("
");
    return OK;
}

status visit(SElemType e)
{
    printf("%d ", e);
    return OK;
}

status StackEmpty(SqStack *s)
{
    if(s->top == s->base)
    {
        printf("栈的状态：栈空
");
        return TRUE;
    }
    else{
        printf("栈的状态：栈非空
");
        return FALSE;
    }
}

int StackLength(SqStack *s)
{
    int len = (int)(s->top - s->base);
    printf("栈的长度：len=%d
", len);
    return 0;
}

status GetTop(SqStack *s, SElemType *e)
{
    if(&s->top == &s->base) return ERROR;
    e = (s->top-1);
    printf("当前栈顶元素：e=%d
", *e);
    return OK;
}

status Clearstack(SqStack *s)
{
    s->top = s->base;
    return OK;
}

status Destorystack(SqStack *s)
{
    s->base = s->top = NULL;
    s->stacksize = 0;
    free(s->base);
    printf("栈被销毁:top = %d, base= %d, stacksize = %u
",s->top,s->base,s->stacksize);
    return OK;
}

六、打印结果

栈中的元素依次为：1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 
弹出的栈顶元素 e=20
当前栈顶元素：e=19
栈的状态：栈非空
栈的长度：len=19
栈的状态：栈空
栈被销毁:top = 0, base= 0, stacksize = 0
Program ended with exit code: 0