Compilare: user.cpp: In function ‘long long unsigned int inversions(int, int)’: user.cpp:6:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (dp[n][k] != -1) return dp[n][k]; ^ user.cpp: In function ‘int main()’: user.cpp:16:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("perm6.in", "r", stdin); ^ user.cpp:17:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("perm6.out", "w", stdout); ^ user.cpp:19:30: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d", &n, &k); ^