View Compilation Error

0_0_18812399_14096.cpp:17:18: error: 'dp' does not name a type
 LL dp[20][20][2];dp[len][sum][tag]//前len 位，到当前为为止有num 个tag, tag=0 表示偶数，1为奇数
                  ^
0_0_18812399_14096.cpp: In function 'LL solve(LL)':
0_0_18812399_14096.cpp:56:31: error: 'dfs' was not declared in this scope
     return dfs(len, 0, 0, 0, 0);
                               ^