题目链接 

草稿上写的规律很明显了。

#include<cstdio>
#include <cstring>
#include<algorithm>
#include <iostream>
using namespace std;
int a[100]={0,0,0,0,0,3,4};

void init()//预处理n2的长度，存放在数组a中
{
    for(int i = 7 ;i < 100;i += 3)
    {
        a[i] = (i + 2) / 3;
    }
    for(int i = 8 ;i < 100;i += 3)
    {
        a[i] = a[i - 1] + 1;
    }
    for(int i = 9 ;i < 100;i += 3)
    {
        a[i] = a[i - 1] + 1;
    }
}
int main()
{
    char str[100];
    init();
    while(scanf("%s",str)!=EOF){
    
        int len = strlen(str);
        int bsnum = a[len] - 2;//空格数
        int vernum = (len - a[len]) / 2;  //要输出有空格的行数有几行
        for(int i = 0 ;i < vernum ;i++)
        {
            printf("%c",str[i]);
            for(int j = 0; j < bsnum;j++)
                printf(" ");
            printf("%c\n",str[len - 1 - i]);
        }
        for(int i = vernum; i <= vernum + a[len] - 1;i++ )
            printf("%c",str[i]);
        printf("\n");
   }

    return 0;
}