C++面试题－－（六）

Write C/C++ program which will repeatedly prompt for and read command from the terminal and perform desired action.
The commands to be supported are:

Add an item into the queue at a given priority, e.g.
Priority: 1
Item:item 1
Print the current contents of the queue.
1: item 1, next item, …
…
9: my item, …
Reverse – toggle the priority order of the queue, e.g.
9: my item, …
…
1: item 1, next item, …
Remove the highest priority item form the queue and print it, e.g.
Removed: my item

Specifications of the priority queue:
·Items added into queue may have priority in range 0 to 9
·Initially, 0 is the highest priority.
·Within one priority level, items should be maintained as FIFO.
Hints:
· It is not imperative that you complete application.
· Parts of application you did not finished comment:
1.Why did you not implement?
2.How would you implement?
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#include <stdio.h> 
#include <stdlib.h> 
#include <string.h> 

#define FALSE   0 
#define TRUE    1 

typedef int     BOOL; 

struct item { 
        char    *info; 
        struct item     *next; 
}; 

struct item     *queue[10]; 

BOOL swcmd(int); 
void add_item(int priority, char *buf); 
void print_item(void); 
void rm_item(void); 
struct item     *get_last_item(int priority);           // get the last item with the priority. 
void free_item(struct item *tmp); 
void flush_in(void);                    // to flush input buffer. 

int main(void) { 
        int     ch, loop = TRUE; 
        while (loop) { 
                printf("type a command to run the program(h for help): "); 
                ch = getchar(); 
                flush_in(); 
                loop = swcmd(ch); 
        } 
        exit(0); 
} 

/**//* 
* to process the different command. 
* 
*/ 
BOOL swcmd(int ch) { 
        BOOL    ret = TRUE; 
        int     priority; 
        char    buf[256]; 
        switch (ch) { 
                case 'a' : 
                        printf("add an item.\n"); 
                        printf("priority: "); 

                        scanf("%d", &priority); 
                        flush_in(); 
                        if ((priority < 0) || (priority > 9)) { 
                                printf("priority must be in 0 to 9.\n"); 
                                break; 
                        } 

                        printf("item: "); 
                        scanf("%s", buf); 
                        flush_in(); 
                        add_item(priority, buf);        // maybe unsucessful. 
                        break; 
                case 'p' : 
                        printf("print the items.\n"); 
                        print_item(); 
                        break; 
                case 'o' : 
                        rm_item(); 
                        break; 
                case 'h' : 
                        printf("a -- add an item to the queue.\n"); 
                        printf("p -- print the queue.\n"); 
                        printf("o -- take out the highest priority item.\n"); 
                        printf("h -- show this help information.\n"); 
                        printf("q -- quit this program.\n"); 
                        break; 
                case 'q' : 
                        ret = FALSE; 
                        break; 
                default : 
                        printf("an unrecgnized command!\n"); 
        } 
        return ret; 
} 

/**//* 
* add an item to the date structure. 
* 
*/ 
void add_item(int priority, char *buf) { 
        struct item     *tmp, *last; 

        tmp = (struct item *)malloc(sizeof(struct item)); 
        if (tmp == NULL) { 
                perror("add_item::malloc"); 
                exit(1); 
        } 

        tmp->info = strdup(buf); 
        if (tmp->info == NULL) { 
                perror("add_item::strdup"); 
                exit(1); 
        } 

        tmp->next = NULL; 
        last = get_last_item(priority); 
        if (last == NULL) { 
                queue[priority] = tmp; 
                return; 
        } 

        last->next = tmp; 
        return; 
} 

/**//* 
* to show the items on the screen. 
* 
*/ 
void print_item(void) { 
        int     i; 
        struct item     *tmp; 
        for (i = 0; i < 10; i++) { 
                printf("%d: ", i); 
                tmp = queue[i]; 
                while (tmp != NULL) { 
                        printf("%s, ", tmp->info); 
                        tmp = tmp->next; 
                } 
                printf("-\n"); 
        } 
        return ; 
} 

/**//* 
* get the last item position with the same priority. 
* 
*/ 
struct item *get_last_item(int priority) { 
        struct item     *tmp; 
        tmp = queue[priority]; 
        if (tmp == NULL) { 
                return tmp; 
        } 
        while (tmp->next != NULL) { 
                tmp = tmp->next; 
        } 
        return tmp; 
} 

/**//* 
* output the highest priority item,and remove it from the queue. 
* 
*/ 
void rm_item(void) { 
        int     i; 
        struct item     *tmp; 
        for (i = 9; i >= 0; i--) { 
                if (queue[i] == NULL) { 
                        continue; 
                } 
                tmp = queue[i]; 
                queue[i] = tmp->next; 
                break; 
        } 

        if (i < 0) {            // a trap to remove nothing. 
                return; 
        } 

        printf("the highest priority item: [%d] %s\n", i, tmp->info); 
        free_item(tmp); 
        print_item(); 
        return; 
} 

/**//* 
* to free the struct item. 
* 
*/ 
void free_item(struct item *tmp) { 
        free(tmp->info); 
        free(tmp); 
} 

/**//* 
* to flush the input buffer. 
* 
*/ 
void flush_in(void) { 
        int     ch; 
        ch = getchar(); 
        while (ch != '\n') { 
                ch = getchar(); 
        } 
        return ; 
}