Only reserve output size in path::walk

include/tc/core.hpp

@@ -6,13 +6,6 @@
 #include <string>
 
 namespace tc {
-    struct Action;
-    struct Path;
-    struct Cosets;
-    struct Rel;
-    struct Group;
-    struct SubGroup;
-
     struct Action {
         int from_idx = -1;
         int gen = -1;
@@ -25,10 +18,9 @@ namespace tc {
     };
 
     struct Path {
-        const tc::Group &context;
         std::vector<Action> path;
 
-        explicit Path(const tc::Group &context);
+        Path() = default;
 
         Path(const Path &) = default;
 
@@ -37,6 +29,25 @@ namespace tc {
         [[nodiscard]] Action get(int to_idx) const;
 
         void put(int from_idx, int gen, int to_idx);
+      
+        template<class C, class T, class E>
+        void walk(
+            C& res,
+            T start,
+            std::vector<E> gens,
+            std::function<T(const T &, const E &)> op
+        ) const {
+            size_t s = size();
+            res.reserve(s);
+            res.push_back(start);
+
+            for (int i = 1; i < s; ++i) {
+                auto &action = path[i];
+                auto &from = res.get(action.from_idx);
+                auto &val = gens[action.gen];
+                res.push_back(op(from,val));
+            }
+        }
 
         template<class T, class E>
         [[nodiscard]] std::vector<T> walk(
@@ -44,14 +55,15 @@ namespace tc {
             std::vector<E> gens,
             std::function<T(const T &, const E &)> op
         ) const {
-            std::vector<T> res(size());
-            res[0] = start;
+            std::vector<T> res;
+            res.reserve(size());
+            res.push_back(start);
 
-            for (int i = 1; i < res.size(); ++i) {
+            for (int i = 1; i < size(); ++i) {
                 auto &action = path[i];
                 auto &from = res[action.from_idx];
                 auto &val = gens[action.gen];
-                res[i] = op(from, val);
+                res.push_back(op(from, val));
             }
 
             return res;
@@ -62,10 +74,11 @@ namespace tc {
             T start,
             std::function<T(const T &, const int &)> op
         ) const {
-            std::vector<T> res(size());
-            res[0] = start;
+            std::vector<T> res;
+            res.reserve(size());
+            res.push_back(start);
 
-            for (int i = 1; i < res.size(); ++i) {
+            for (int i = 1; i < size(); ++i) {
                 auto &action = path[i];
                 auto &from = res[action.from_idx];
                 auto &val = action.gen;
@@ -79,14 +92,13 @@ namespace tc {
     };
 
     struct Cosets {
-        const tc::Group &context;
-
+        int ngens;
         std::vector<int> data;
         Path path;
 
         Cosets(const Cosets &) = default;
 
-        explicit Cosets(const tc::Group &context);
+        explicit Cosets(int ngens);
 
         void add_row();
 
@@ -114,8 +126,10 @@ namespace tc {
         [[nodiscard]] Rel shift(int off) const;
     };
 
+    struct SubGroup;
+
     struct Group {
-        const int ngens;
+        int ngens;
         std::vector<std::vector<int>> _mults;
         std::string name;
 

src/core.cpp

@@ -9,10 +9,6 @@ namespace tc {
         : from_idx(from_idx), gen(gen) {
     }
 
-    Path::Path(const tc::Group &context)
-        : context(context), path() {
-    }
-
     void Path::add_row() {
         path.resize(path.size() + 1);
     }
@@ -29,18 +25,18 @@ namespace tc {
         return path.size();
     }
 
-    Cosets::Cosets(const tc::Group &context)
-        : path(context), context(context), data() {
+    Cosets::Cosets(int ngens)
+        : ngens(ngens) {
     }
 
     void Cosets::add_row() {
-        data.resize(data.size() + context.ngens, -1);
+        data.resize(data.size() + ngens, -1);
         path.add_row();
     }
 
     void Cosets::put(int coset, int gen, int target) {
-        data[coset * context.ngens + gen] = target;
-        data[target * context.ngens + gen] = coset;
+        data[coset * ngens + gen] = target;
+        data[target * ngens + gen] = coset;
 
         if (path.get(target).from_idx == -1) {
             path.put(coset, gen, target);
@@ -48,10 +44,10 @@ namespace tc {
     }
 
     void Cosets::put(int idx, int target) {
-        int coset = idx / context.ngens;
-        int gen = idx % context.ngens;
+        int coset = idx / ngens;
+        int gen = idx % ngens;
         data[idx] = target;
-        data[target * context.ngens + gen] = coset;
+        data[target * ngens + gen] = coset;
 
         if (path.get(target).from_idx == -1) {
             path.put(coset, gen, target);
@@ -59,7 +55,7 @@ namespace tc {
     }
 
     int Cosets::get(int coset, int gen) const {
-        return data[coset * context.ngens + gen];
+        return data[coset * ngens + gen];
     }
 
     int Cosets::get(int idx) const {

src/solve.cpp

@@ -65,7 +65,7 @@ namespace tc {
     };
 
     Cosets Group::solve(const std::vector<int> &sub_gens) const {
-        Cosets cosets(*this);
+        Cosets cosets(ngens);
         cosets.add_row();
 
         if (ngens == 0) {