: static NODE *block_append(NODE *head, NODE *tail)
    head  tail  NODE_BLOCK ΥꥹȤȤϢ뤷
    ƬΡɤ֤ޤhead ޤ tail  NODE_BLOCK
    Ǥʤ NODE_BLOCK 줿ǤϢ뤷ޤ
    head ⤷ tail  NULL ʤϢϤ
    NULL Ǥʤ֤ۤޤ

