foo.cc:2:21: error: expected unqualified-id before '!' token
 using namespace std;![](http://)
                     ^
foo.cc: In function 'bool dfs(int)':
foo.cc:15:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int j = 0; j < edges[i].size(); j++) {
                     ~~^~~~~~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:31:21: error: 'n' was not declared in this scope
     scanf("%d %d", &n, &m);
                     ^
foo.cc:31:25: error: 'm' was not declared in this scope
     scanf("%d %d", &n, &m);
                         ^
foo.cc:43:27: warning: suggest parentheses around comparison in operand of '^' [-Wparentheses]
             if (arr[i][j] == 1 ^ (((i + j) & 1) == ((x + y) & 1)))
                 ~~~~~~~~~~^~~~
foo.cc:34:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%s", str + 1);
         ~~~~~^~~~~~~~~~~~~~~
foo.cc:63:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &k);
     ~~~~~^~~~~~~~~~
foo.cc:73:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d %d", &x, &y);
         ~~~~~^~~~~~~~~~~~~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。