stack

stack是一种先进后出的数据结构。

stack主要操作为，入栈，出栈，判断栈空满等。

1. 数组实现栈

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>

#define MAX 10

int arr[MAX];
int pos = 0;

void push(int value)
{
    arr[pos ++] = value;
}

int pop(void)
{
    return arr[-- pos];
}

bool is_empty(void)
{
    return pos == 0;
}

bool is_full(void)
{
    return pos == MAX;
}

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

    while((ch = getchar()) != '\n') {
        if (! is_full()) {
            push(ch);
        }
    }

    while(! is_empty()) {
        putchar(pop());
    }
    return 0;
}

2. 数组栈

#ifndef _STACK_H_
#define _STACK_H_

#include <stdbool.h>

#define MAX 10

typedef struct stack {
    int arr[MAX];
    int pos;
} Stack;

extern void stack_init(Stack *stack);
extern void stack_push(Stack *stack, int value);
extern int stack_pop(Stack *stack);
extern bool stack_is_empty(Stack *stack);
extern bool stack_is_full(Stack *stack);

#endif    //_STACK_H_

#include "stack.h"

void stack_init(Stack *stack)
{
    stack->pos = 0;
}

void stack_push(Stack *stack, int value)
{
    stack->arr[stack->pos ++] = value;
}
int stack_pop(Stack *stack)
{
    return stack->arr[-- stack->pos];
}
bool stack_is_empty(Stack *stack)
{
    return stack->pos == 0;
}
bool stack_is_full(Stack *stack)
{
    return stack->pos == MAX;
}

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>

#include "stack.h"

bool is_digit(char ch)
{
    if (ch >= '0' && ch <= '9') {
        return true;
    } 
    return false;
}

int main(int argc, char *argv[])
{
    char ch;
    Stack s1, s2;

    stack_init(&s1);
    stack_init(&s2);

    while((ch = getchar()) != '\n') {
        if (is_digit(ch)) {
            if (! stack_is_full(&s1)) {
                stack_push(&s1, ch);
            }
        } else {
            if (! stack_is_full(&s2)) {
                stack_push(&s2, ch);
            }
        }
    }    

    while(! stack_is_empty(&s1)) {
        putchar(stack_pop(&s1));
    }
    
    putchar('\n');

    while(! stack_is_empty(&s2)) {
        putchar(stack_pop(&s2));
    }

    return 0;
}

3. 链表栈

#ifndef _STACK_H_
#define _STACK_H_

#include <stdbool.h>

struct node {
    void *data;
    struct node *next;
};

typedef struct {
    struct node *top;
} Stack;

extern void stack_init(Stack *stack);
extern void stack_push(Stack *stack, void *data);
extern void *stack_pop(Stack *stack);
extern bool stack_is_empty(Stack *stack);
extern bool stack_is_full(Stack *stack);
extern void stack_destroy(Stack *stack,
        void (*destroy)(void *data));

#endif    //_STACK_H_

#include <stdlib.h>
#include <assert.h>

#include "stack.h"

void stack_init(Stack *stack)
{
    stack->top = NULL;
}

static struct node * make_node(void *data)
{
    struct node *n;

    n = malloc(sizeof(struct node));
    assert(n);
    n->data = data;
    n->next = NULL;

    return n;
}

void stack_push(Stack *stack, void *data)
{
    struct node *n;
    
    n = make_node(data);    
/*
    if (stack->top == NULL) {
        stack->top = n;
    } else {
        n->next = stack->top;
        stack->top = n;
    }
*/
    n->next = stack->top;
    stack->top = n;
}

void *stack_pop(Stack *stack)
{
    void *data;
    struct node *n;
    
    n = stack->top;
    stack->top = n->next;
    data = n->data;
    free(n);
    return data;
}
bool stack_is_empty(Stack *stack)
{
    return stack->top == NULL;
}
bool stack_is_full(Stack *stack)
{
    return false;
}

void stack_destroy(Stack *stack,
        void (*destroy)(void *data))
{
    while(! stack_is_empty(stack)) {
        if (destroy) {
            destroy(stack_pop(stack));
        } else {
            stack_pop(stack);
        }
    }    
}

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

#include "stack.h"

void destroy_data(void *data)
{
    char *p = data;
    free(p);
}

int main(int argc, char *argv[])
{
    char ch;
    char *p;
    Stack s;

    stack_init(&s);

    while((ch = getchar()) != '\n') {
        p = malloc(sizeof(char));
        assert(p);
        *p = ch;

        if (! stack_is_full(&s)) {
            stack_push(&s, p);
        }
    }

    while(! stack_is_empty(&s)) {
        p = stack_pop(&s);
        putchar(*p);
        free(p);
    }
    stack_destroy(&s, destroy_data);
    return 0;
}