题解 | #MP3光标位置#

#include <stdio.h>

int cmd_up(int *current, int* cmd_up, int* cmd_down, int songs)
{
    int flag = 0;
    /* 首先移动当前歌曲光标位置 */
    if(*current == 1)
    {
        (*current) = songs;
        flag = 1;
    }
    else
    {
        (*current)--;
    }
    
    /* 当前歌曲为特殊翻页，到歌曲末尾 */
    if(flag == 1)
    {
        /* 总歌曲数小于4， UP置为1 */
        if(songs < 4)
        {
            *cmd_up = 1;
        }
        else    /* 总歌曲数大于等于4，UP置为歌曲倒数第四首 */
        {
            (*cmd_up) = (songs - 4 + 1);   
        }
        
        (*cmd_down) = songs;
    }
    else if(*current < *cmd_up)        /* 当前歌曲光标超过 Up时， 当前显示列表向上移动 */
    {
        if(*cmd_up == 1)
        {
            (*cmd_up) = songs;
        }
        else
        {
            (*cmd_up)--;
        }
        
        if(*cmd_down == 1)
        {
            (*cmd_down) = songs;
        }
        else
        {
            (*cmd_down)--;
        }
    }
    
    return 0;
}

int cmd_down(int *current, int* cmd_down, int* cmd_up, int songs)
{
    int flag = 0;
    if(*current == songs)
    {
        (*current) = 1;
        flag = 1;
    }
    else
    {
        (*current)++;
    }
    
    if(flag == 1)
    {
        if(songs < 4)
        {
            *cmd_down = songs;
        }
        else
        {
            *cmd_down = 4;
        }
        
        *cmd_up = 1;
    }
    else if(*current > *cmd_down)
    {
         if(*cmd_down == songs)
        {
            (*cmd_down) = 1;
        }
        else
        {
            (*cmd_down)++;
        }
        
         if(*cmd_up == songs)
         {
             (*cmd_up) = 1;
         }
        else
        {
            (*cmd_up)++;
        }
    }
    return 0;
}


int main()
{
    int songs;
    char cmd[101] = {0};
    
    if(scanf("%d", &songs) != EOF)
    {
        int up = 1;
        int down = 4;
        int current = 1;
        
        scanf("%s", cmd);
        
        for(int i = 0; i < strlen(cmd); i++)
        {
            if(cmd[i] == 'U')
            {
                /* UP上一首 */
                cmd_up(&current, &up, &down, songs);
                
            }
            else if(cmd[i] == 'D')
            {
                /* DOWN下一首 */
                cmd_down(&current, &down, &up, songs); 
            }
//             printf("up = %d, down = %d, current = %d \n", up, down, current);        
        }
       
        for(int i = 0; i < 4 && i < songs; i++)
        {
            if(up > songs)
            {
                up = 1;
                printf("%d ", up++);
            }
            else
            {
                printf("%d ", up++);
            }
        }
        
        printf("\n%d", current);    
    }
    
    return 0;
}