Compilare: user.cpp: In function ‘void add(Trie*, char*)’: user.cpp:24:13: warning: NULL used in arithmetic [-Wpointer-arith] if (*s == NULL) { ^~~~ user.cpp: In function ‘void solve(Trie*)’: user.cpp:38:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (root->sons[i]->dp.size() > ans) { ~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~ user.cpp:59:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (root->dp.size() <= k) ~~~~~~~~~~~~~~~~^~~~ user.cpp: In function ‘int main()’: user.cpp:72:32: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("cli.in", "r", stdin); ^ user.cpp:73:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("cli.out", "w", stdout); ^ user.cpp:77:25: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d ", &n, &k); ^ user.cpp:79:19: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%s", s); ^