Apply code simplification improvements

- Consolidated two contains() methods into single template function
- Added const correctness to helper methods in argument_parser.h
- Improved string handling (replaced substr with compare, return "" instead of std::string())
- Fixed indentation in nlsat_solver.cpp nested loop
- Modernized empty container return syntax in lp.cpp

Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

src/nlsat/nlsat_solver.cpp

@@ -1208,8 +1208,8 @@ namespace nlsat {
                     used_bools[b] = true;
                 vars.reset();
                 this->vars(lit, vars);
-            for (var v : vars)
-                        used_vars[v] = true;            
+                for (var v : vars)
+                    used_vars[v] = true;            
             }
             display(out << "(echo \"#" << m_lemma_count++ << ":" << annotation << ":", n, cls) << "\")\n";
             if (m_log_lemma_smtrat)

src/test/lp/argument_parser.h

@@ -82,11 +82,8 @@ public:
         return status_is_ok;
     }
 
-    bool contains(std::unordered_map<std::string, std::string> & m, const std::string& s) {
-        return m.find(s) != m.end();
-    }
-
-    bool contains(std::set<std::string> & m, const std::string& s) {
+    template<typename Container>
+    bool contains(const Container& m, const std::string& s) const {
         return m.find(s) != m.end();
     }
 
@@ -94,22 +91,22 @@ public:
         return contains(m_used_options, option) || contains(m_used_options_with_after_string, option);
     }
 
-    std::string get_option_value(const std::string& option) {
+    std::string get_option_value(const std::string& option) const {
         auto t = m_used_options_with_after_string.find(option);
-        if (t != m_used_options_with_after_string.end()){
+        if (t != m_used_options_with_after_string.end()) {
             return t->second;
         }
-        return std::string();
+        return "";
     }
 
-    bool starts_with(const std::string& s, char const * prefix) {
+    bool starts_with(const std::string& s, const std::string& prefix) const {
+        return s.size() >= prefix.size() && s.compare(0, prefix.size(), prefix) == 0;
+    }
+
+    bool starts_with(const std::string& s, const char* prefix) const {
         return starts_with(s, std::string(prefix));
     }
 
-    bool starts_with(const std::string& s, const std::string& prefix) {
-        return s.substr(0, prefix.size()) == prefix;
-    }
-
     std::string usage_string() {
         std::string ret = "";
         std::vector<std::string> unknown_options;

src/test/lp/lp.cpp

@@ -732,7 +732,7 @@ vector<std::string> get_file_names_from_file_list(const std::string& filelist) {
     std::ifstream file(filelist);
     if (!file.is_open()) {
         std::cout << "cannot open " << filelist << std::endl;
-        return vector<std::string>();
+        return {};
     }
     vector<std::string> ret;
     bool end;