View Compilation Error

0_0_13906806_9258.cpp: In function 'LL dfs(int, int, int, int)':
0_0_13906806_9258.cpp:52:24: error: 'k' was not declared in this scope
     if(!e && f[len][s][k] != -1) return f[len][s][k];
                        ^
0_0_13906806_9258.cpp:60:22: error: 'k' was not declared in this scope
     if(!e) f[len][s][k] = ans;
                      ^