View Compilation Error

0_0_12073391_13694.cpp: In function `void dfs(int, int, int)':
0_0_12073391_13694.cpp:29: error: `max_len' undeclared (first use this function)
0_0_12073391_13694.cpp:29: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_12073391_13694.cpp: In function `int main()':
0_0_12073391_13694.cpp:45: error: `max_len' undeclared (first use this function)