/in/foo.cc: In function 'bool dfs(int)':
/in/foo.cc:15:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int j = 0; j < edges[i].size(); j++) {
                     ~~^~~~~~~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:43:27: warning: suggest parentheses around comparison in operand of '^' [-Wparentheses]
             if (arr[i][j] == 1 ^ (((i + j) & 1) == ((x + y) & 1)))
                 ~~~~~~~~~~^~~~