HDU 4731 Minimum palindrome （找规律）

M=1：aaaaaaaa……

M=2：DFS+manacher， 暴出N=1~25的最优解，找规律。N<=8的时候直接输出，N>8时，头两个字母一定是aa，剩下的以aababb循环，最后剩余<5全部补a，等于5补aabab。

M=3：abcabcabcabc……

#include <cstdio>
#include <cstring>

using namespace std;

const char str[] = "aababb";

int main()
{
    int T;
    int cas = 0;
    scanf( "%d", &T );
    while ( T-- )
    {
        int M, N;
        scanf( "%d%d", &M, &N );
        printf("Case #%d: ", ++cas );
        if ( M == 1 )
        {
            for ( int i = 0; i < N; ++i )
                putchar('a');
            puts("");
        }
        else if ( M == 2 )
        {
            int cnt;
            switch( N )
            {
                case 1: puts("a"); break;
                case 2: puts("ab"); break;
                case 3: puts("aab"); break;
                case 4: puts("aabb"); break;
                case 5: puts("aaaba"); break;
                case 6: puts("aaabab"); break;
                case 7: puts("aaababb"); break;
                case 8: puts("aaababbb"); break;
                default:
                N -= 2;
                printf("aa");
                cnt = N / 6;
                for ( int i = 0; i < cnt; ++i )
                    printf( "%s", str );
                N -= cnt*6;
                if ( N < 5 )
                {
                    for ( int i = 0; i < N; ++i )
                    putchar('a');
                    puts("");
                }
                else puts("aabab");

            }
        }
        else
        {
            int j = 0;
            for ( int i = 0; i < N; ++i )
            {
                putchar( 'a' + j );
                ++j;
                if ( j > 2 ) j = 0;
            }
            puts("");
        }
    }
    return 0;
}