6、栈

1、顺序栈

#include<stdio.h>
#include<malloc.h>
#include<assert.h>

#define ElemType int

#define STACK_INIT_SIZE 8
#define STACK_INC_SIZE  3


//顺序栈的定义 
typedef struct SeqStack{
    ElemType *base;
    int       capacity;
    int       top;    
}SeqStack;

//初始化顺序栈 
void init_SeqStack(SeqStack* st){
    st->base = (ElemType*)malloc(sizeof(ElemType) * STACK_INIT_SIZE);
    st->capacity = STACK_INIT_SIZE;
    /*
    top可为 -1 [入栈:先top++在放值 出栈: 先取值在top--] 
       也可为 0 [入栈:先放值在++ 出栈: 先--在放值] 
    */
    st->top = 0;
}

//判断栈是否已满[为真返回1 为假返回0 ] 
int isFull(SeqStack* st){
    return st->top >= st->capacity;
}

//判断栈是否为空[为真返回1 为假返回0 ]
int isEmpty(SeqStack* st){
    return st->top == 0;
}

int inc_stack(SeqStack* st){
    ElemType* newBase = (ElemType*)realloc(st->base,sizeof(ElemType) * (st->capacity + STACK_INC_SIZE));
    if(newBase == NULL){
        printf("内存空间不足,无法申请空间.\n");
        return 0;
    }
    st->base = newBase;
    st->capacity += STACK_INC_SIZE;
    return 1;
}

//入栈
void push(SeqStack* st,ElemType e){
    if(isFull(st) && !inc_stack(st)){
        printf("栈空间已满,%d 不能入栈.\n",e);
        return;
    }
    //如果top为-1 =>  st->base[++st->top] = e;
    st->base[st->top++] = e;
}

//出栈
ElemType pop(SeqStack* st){
    if(isEmpty(st)){
        printf("栈空间已空,不能出栈.\n");
        return;
    } 
    //如果top为-1 =>  return st->base[st->top--];
    return st->base[--st->top]; 
} 

//得到栈顶元素，但不出栈
ElemType get_top(SeqStack* st){
    if(isEmpty(st)){
        printf("栈空间已空,不能出栈.\n");
        return;
    } 
    return st->base[st->top - 1];
}

//栈的长度
int length(SeqStack* st){
    return st->top;
} 

//清空栈
void clear(SeqStack* st){
    st->top = 0;
}

//销毁栈
void destroy(SeqStack* st){
    free(st->base);
    st->capacity = st->top = 0;
} 

//打印栈
void show_stack(SeqStack* st){
    int i = st->top - 1;
    for(i;i >= 0;i--){
        printf("%d\n",st->base[i]);
    }
    printf("\n");
}
int main(){
    SeqStack st;
    init_SeqStack(&st);
    int i = 1;
    for(i;i <= 5;i++){
        push(&st,i);
    }
    show_stack(&st);
    pop(&st);
        show_stack(&st);

    return 0;
} 

2、链栈

#include<stdio.h>
#include<malloc.h>
#include<assert.h>

#define ElemType int

typedef struct StackNode{
    ElemType data;
    struct StackNode* next;
}StackNode;

typedef StackNode* LinkStack;

//注意 这里是二级指针 
void initStack(LinkStack* st){
    st = NULL;
}

StackNode* malloc_statckNode(ElemType e){
    StackNode* p = (StackNode*)malloc(sizeof(StackNode));
    assert(p != NULL);
    p->data = e;
    p->next = NULL;
} 

//入栈 
void push(LinkStack* st,ElemType e){
    StackNode* p = malloc_statckNode(e);
    if(*st == NULL){
        //当前栈空间为空 ,新节点直接为栈顶 
        *st = p;
    } else {
        //新节点指向栈顶 
        p->next = *st;
        //更换栈顶 
        *st = p;
    }
} 

//出栈
ElemType pop(LinkStack* st) {
    if(*st == NULL){
        printf("当前栈空间为空,不可出栈.\n"); 
        return;
    }
    StackNode* top = *st;
    *st = top->next;
    ElemType e = top->data;
    free(top);
    return e;
}
//打印栈
void show(LinkStack* st){
    LinkStack s = *st;
    while(s != NULL){
        printf("%d\n",s->data);
        s = s->next;
    }
    printf("\n");
}
int main(){
    LinkStack st;
    //二级指针接收一级指针的地址 
    initStack(&st);
    int i = 1;
    for(i;i <= 5;i++){
        push(&st,i);
    }
    show(&st);
    pop(&st);
    show(&st);

    return 0;
}