diff --git a/1-data-structure/fenwick_tree.cpp b/refcode/1-ds/fenwick_tree.hpp
similarity index 97%
rename from 1-data-structure/fenwick_tree.cpp
rename to refcode/1-ds/fenwick_tree.hpp
index 2af83ac..ace7525 100644
--- a/1-data-structure/fenwick_tree.cpp
+++ b/refcode/1-ds/fenwick_tree.hpp
@@ -1,5 +1,5 @@
 #include "../common/common.hpp"
-
+namespace refcode {
 // 1. Fenwick Tree
 struct Fenwick { // 0-indexed
   int flag, cnt; // array size
@@ -23,7 +23,7 @@ struct Fenwick { // 0-indexed
   }
   void modify(int p, ll value) { // set value at position p
     add(p, value - arr[p]);
-  };
+  }
   ll query(int x) {
     ll ret = 0;
     while (x >= 0) ret += t[x], x = (x & (x + 1)) - 1;
@@ -43,10 +43,9 @@ struct Fenwick { // 0-indexed
     }
     return l;
   }
-} fw;
-
+};
 // 2. Fenwick Tree Range Update Point Query
-struct Fenwick { // 1-indexed
+struct FenwickRUPQ { // 1-indexed
   int flag;
   vector<ll> t;
   void build(int N) {
@@ -62,8 +61,7 @@ struct Fenwick { // 1-indexed
     for (; x; x ^= x & -x) ret += t[x];
     return ret;
   }
-} fw;
-
+};
 // 3. 2D Fenwick Tree
 // INPUT: Given an 2D array of integers of size N * M.
 // Can modify the value of the (x, y)th element.
@@ -130,4 +128,5 @@ struct Fenwick2D { // 0-indexed
     if (sx && sy) ret += query(sx - 1, sy - 1);
     return ret;
   }
-} fw2d;
\ No newline at end of file
+};
+} // namespace refcode
\ No newline at end of file
diff --git a/1-data-structure/li_chao_tree.cpp b/refcode/1-ds/li_chao_tree.hpp
similarity index 93%
rename from 1-data-structure/li_chao_tree.cpp
rename to refcode/1-ds/li_chao_tree.hpp
index 728add8..4fc8b3c 100644
--- a/1-data-structure/li_chao_tree.cpp
+++ b/refcode/1-ds/li_chao_tree.hpp
@@ -1,14 +1,13 @@
 #include "../common/common.hpp"
-
+namespace refcode {
 // INPUT: Initially, a 2d plane in which no linear function exists is given.
 // Two types of queries are given.
 // 1 a b : The linear function f(x) = ax + b is added.
 // 2 x : Find the max(f(x)) among the linear functions given so far.
 // OUTPUT: For each query 2 x, output the max(f(x)) among the linear functions given so far.
 // TIME COMPLEXITY: O(qlogq)
-#define Line pair<ll, ll>
-
-const Line e = {0, -1e18};
+using Line = pair<ll, ll>;
+constexpr Line e = {0, -1e18};
 struct LiChaoTree {
   ll f(Line l, ll x) { return l.first * x + l.second; }
   struct Node {
@@ -56,4 +55,5 @@ struct LiChaoTree {
     else ret = max(ret, query(x, t[n].r));
     return ret;
   }
-} lct;
\ No newline at end of file
+};
+} // namespace refcode
\ No newline at end of file
diff --git a/1-data-structure/merge_sort_tree.cpp b/refcode/1-ds/merge_sort_tree.hpp
similarity index 94%
rename from 1-data-structure/merge_sort_tree.cpp
rename to refcode/1-ds/merge_sort_tree.hpp
index b3c3644..7f330ac 100644
--- a/1-data-structure/merge_sort_tree.cpp
+++ b/refcode/1-ds/merge_sort_tree.hpp
@@ -1,10 +1,10 @@
 #include "../common/common.hpp"
-
+namespace refcode {
+constexpr int MAX_MST = 1 << 17;
 // 1. Merge Sort Tree
 // INPUT: Given a sequence A_1, A_2, ..., A_n of length n. Given a query (i, j, k).
 // OUTPUT: For each query (i, j, k), output the number of elements greater than k among elements A_i, A_{i+1}, ..., A_j.
 // TIME COMPLEXITY: O(nlogn) for initialize Merge Sort Tree, O(log^2n) for each query.
-const int MAX_MST = 1 << 17;
 struct MergeSortTree {
   vector<int> t[MAX_MST << 1];
   void build(const vector<int> &arr) {
@@ -22,14 +22,12 @@ struct MergeSortTree {
     int mid = (nl + nr) >> 1;
     return query(l, r, k, n << 1, nl, mid) + query(l, r, k, n << 1 | 1, mid + 1, nr);
   }
-} mstree;
-
+};
 // 2. Iterative Merge Sort Tree
 // INPUT: Given a sequence A_1, A_2, ..., A_n of length n. Given a query (i, j, k).
 // OUTPUT: For each query (i, j, k), output the number of elements greater than k among elements A_i, A_{i+1}, ..., A_j.
 // TIME COMPLEXITY: O(nlogn) for initialize Merge Sort Tree, O(log^2n) for each query.
-const int MAX_MST = 1 << 17;
-struct MergeSortTree {
+struct MergeSortTreeIter {
   vector<int> t[MAX_MST << 1];
   void build(const vector<int> &arr) {
     for (int i = 0; i < sz(arr); i++)
@@ -49,4 +47,5 @@ struct MergeSortTree {
     }
     return ret;
   }
-} mstree;
\ No newline at end of file
+};
+} // namespace refcode
\ No newline at end of file
diff --git a/1-data-structure/segment_tree.cpp b/refcode/1-ds/segment_tree.hpp
similarity index 95%
rename from 1-data-structure/segment_tree.cpp
rename to refcode/1-ds/segment_tree.hpp
index 13dc4a9..9149260 100644
--- a/1-data-structure/segment_tree.cpp
+++ b/refcode/1-ds/segment_tree.hpp
@@ -1,7 +1,7 @@
 #include "../common/common.hpp"
-
+namespace refcode {
+int flag; // array size
 // 1. Segment Tree
-int flag;    // array size
 struct Seg { // 1-indexed
   vector<ll> t;
   void build(int n) {
@@ -19,12 +19,11 @@ struct Seg { // 1-indexed
     int mid = (nl + nr) / 2;
     return query(l, r, n << 1, nl, mid) + query(l, r, n << 1 | 1, mid + 1, nr);
   }
-} seg;
-
+};
 // 2. Iterative Segment Tree
-const int MAXN = 1010101; // limit for array size
-struct Seg {              // 0-indexed
-  int n;                  // array size
+constexpr int MAXN = 1010101; // limit for array size
+struct SegIter {              // 0-indexed
+  int n;                      // array size
   ll t[2 * MAXN];
   void build(int N) {
     n = N;
@@ -42,11 +41,9 @@ struct Seg {              // 0-indexed
     }
     return ret;
   }
-} seg;
-
+};
 // 3. k-th Segment Tree
-int flag; // array size
-struct Seg {
+struct SegKth {
   vector<ll> t;
   void build(int n) {
     for (flag = 1; flag < n; flag <<= 1);
@@ -61,11 +58,9 @@ struct Seg {
     if (k <= t[n << 1]) return kth(k, n << 1);
     else return kth(k - t[n << 1], n << 1 | 1);
   }
-} seg;
-
+};
 // 4. Segment Tree with Lazy Propagation
-int flag;    // array size
-struct Seg { // 1-indexed
+struct SegLazy { // 1-indexed
   vector<ll> t, lazy;
   void build(int n) {
     for (flag = 1; flag < n; flag <<= 1);
@@ -105,8 +100,7 @@ struct Seg { // 1-indexed
       lazy[n] = 0;
     }
   }
-} seg;
-
+};
 // 5. Persistent Segment Tree
 // TIME COMPLEXITY: O(n) for initialize PST, O(logn) for each query.
 // SPACE COMPLEXITY: O(nlogm).
@@ -153,7 +147,6 @@ struct PST { // 1-indexed
       t[n2].val = val;
       return;
     }
-
     int mid = (l + r) >> 1;
     if (p <= mid) {
       t[n2].r = t[n1].r;
@@ -184,17 +177,14 @@ struct PST { // 1-indexed
     assert(n < sz(root));
     return query(l, r, root[n], 1, flag);
   }
-} pst;
-
+};
 // 6. Dynamic Segment Tree
-const int MAXL = 1, MAXR = 1000000;
-
+constexpr int MAXL = 1, MAXR = 1000000;
 struct Node {
   ll x;
   int l, r;
 };
-
-struct Dyseg {
+struct DySeg {
   vector<Node> t = {{0, -1, -1}, {0, -1, -1}};
   void modify(int p, ll x, int n = 1, int nl = MAXL, int nr = MAXR) {
     if (p < nl || nr < p) return;
@@ -237,4 +227,5 @@ struct Dyseg {
     }
     return ret;
   }
-} dyseg;
+};
+} // namespace refcode
\ No newline at end of file
diff --git a/1-data-structure/union_find.cpp b/refcode/1-ds/union_find.hpp
similarity index 75%
rename from 1-data-structure/union_find.cpp
rename to refcode/1-ds/union_find.hpp
index a63d151..79791ed 100644
--- a/1-data-structure/union_find.cpp
+++ b/refcode/1-ds/union_find.hpp
@@ -1,10 +1,10 @@
 #include "../common/common.hpp"
-
+namespace refcode {
 struct UF {
   vector<int> uf;
-  void build(int N) {
+  void build(int n) {
     uf.clear();
-    uf.resize(N + 1, -1);
+    uf.resize(n + 1, -1);
   }
   int find(int v) {
     if (uf[v] < 0) return v;
@@ -16,4 +16,5 @@ struct UF {
     uf[U] += uf[V];
     uf[V] = U;
   }
-} uf;
\ No newline at end of file
+};
+} // namespace refcode
\ No newline at end of file
diff --git a/2-graph/bcc.cpp b/refcode/2-graph/bcc.cpp
similarity index 100%
rename from 2-graph/bcc.cpp
rename to refcode/2-graph/bcc.cpp
diff --git a/2-graph/dijkstra_bellman_ford_floyd_warshall.cpp b/refcode/2-graph/dijkstra_bellman_ford_floyd_warshall.cpp
similarity index 100%
rename from 2-graph/dijkstra_bellman_ford_floyd_warshall.cpp
rename to refcode/2-graph/dijkstra_bellman_ford_floyd_warshall.cpp
diff --git a/2-graph/euler_circuit.cpp b/refcode/2-graph/euler_circuit.cpp
similarity index 100%
rename from 2-graph/euler_circuit.cpp
rename to refcode/2-graph/euler_circuit.cpp
diff --git a/2-graph/kth_shortest_path.cpp b/refcode/2-graph/kth_shortest_path.cpp
similarity index 100%
rename from 2-graph/kth_shortest_path.cpp
rename to refcode/2-graph/kth_shortest_path.cpp
diff --git a/2-graph/offline_dynamic_connectivity.cpp b/refcode/2-graph/offline_dynamic_connectivity.cpp
similarity index 100%
rename from 2-graph/offline_dynamic_connectivity.cpp
rename to refcode/2-graph/offline_dynamic_connectivity.cpp
diff --git a/2-graph/scc_2_sat.cpp b/refcode/2-graph/scc_2_sat.cpp
similarity index 100%
rename from 2-graph/scc_2_sat.cpp
rename to refcode/2-graph/scc_2_sat.cpp
diff --git a/2-graph/tree_cd.cpp b/refcode/2-graph/tree_cd.cpp
similarity index 100%
rename from 2-graph/tree_cd.cpp
rename to refcode/2-graph/tree_cd.cpp
diff --git a/2-graph/tree_composition.cpp b/refcode/2-graph/tree_composition.cpp
similarity index 100%
rename from 2-graph/tree_composition.cpp
rename to refcode/2-graph/tree_composition.cpp
diff --git a/2-graph/tree_exchange_argument.cpp b/refcode/2-graph/tree_exchange_argument.cpp
similarity index 100%
rename from 2-graph/tree_exchange_argument.cpp
rename to refcode/2-graph/tree_exchange_argument.cpp
diff --git a/2-graph/tree_hld.cpp b/refcode/2-graph/tree_hld.cpp
similarity index 100%
rename from 2-graph/tree_hld.cpp
rename to refcode/2-graph/tree_hld.cpp
diff --git a/2-graph/tree_lca_sparse_table.cpp b/refcode/2-graph/tree_lca_sparse_table.cpp
similarity index 100%
rename from 2-graph/tree_lca_sparse_table.cpp
rename to refcode/2-graph/tree_lca_sparse_table.cpp
diff --git a/3-network-flow/bipartite_matching.cpp b/refcode/3-flow/bipartite_matching.cpp
similarity index 100%
rename from 3-network-flow/bipartite_matching.cpp
rename to refcode/3-flow/bipartite_matching.cpp
diff --git a/3-network-flow/dinics_algorithm.cpp b/refcode/3-flow/dinics_algorithm.cpp
similarity index 100%
rename from 3-network-flow/dinics_algorithm.cpp
rename to refcode/3-flow/dinics_algorithm.cpp
diff --git a/3-network-flow/hopcroft_karp_algorithm.cpp b/refcode/3-flow/hopcroft_karp_algorithm.cpp
similarity index 100%
rename from 3-network-flow/hopcroft_karp_algorithm.cpp
rename to refcode/3-flow/hopcroft_karp_algorithm.cpp
diff --git a/3-network-flow/maximum_flow.cpp b/refcode/3-flow/maximum_flow.cpp
similarity index 100%
rename from 3-network-flow/maximum_flow.cpp
rename to refcode/3-flow/maximum_flow.cpp
diff --git a/3-network-flow/mcmf.cpp b/refcode/3-flow/mcmf.cpp
similarity index 100%
rename from 3-network-flow/mcmf.cpp
rename to refcode/3-flow/mcmf.cpp
diff --git a/4-string/aho_corasick.cpp b/refcode/4-string/aho_corasick.cpp
similarity index 100%
rename from 4-string/aho_corasick.cpp
rename to refcode/4-string/aho_corasick.cpp
diff --git a/4-string/kmp_algorithm.cpp b/refcode/4-string/kmp_algorithm.cpp
similarity index 100%
rename from 4-string/kmp_algorithm.cpp
rename to refcode/4-string/kmp_algorithm.cpp
diff --git a/4-string/manachers_algorithm.cpp b/refcode/4-string/manachers_algorithm.cpp
similarity index 100%
rename from 4-string/manachers_algorithm.cpp
rename to refcode/4-string/manachers_algorithm.cpp
diff --git a/4-string/rabin_karp_algorithm.cpp b/refcode/4-string/rabin_karp_algorithm.cpp
similarity index 100%
rename from 4-string/rabin_karp_algorithm.cpp
rename to refcode/4-string/rabin_karp_algorithm.cpp
diff --git a/4-string/suffix_array.cpp b/refcode/4-string/suffix_array.cpp
similarity index 100%
rename from 4-string/suffix_array.cpp
rename to refcode/4-string/suffix_array.cpp
diff --git a/4-string/trie.cpp b/refcode/4-string/trie.cpp
similarity index 100%
rename from 4-string/trie.cpp
rename to refcode/4-string/trie.cpp
diff --git a/4-string/z_algorithm.cpp b/refcode/4-string/z_algorithm.cpp
similarity index 100%
rename from 4-string/z_algorithm.cpp
rename to refcode/4-string/z_algorithm.cpp
diff --git a/5-geometry/bulldozer_trick.cpp b/refcode/5-geometry/bulldozer_trick.cpp
similarity index 100%
rename from 5-geometry/bulldozer_trick.cpp
rename to refcode/5-geometry/bulldozer_trick.cpp
diff --git a/5-geometry/ccw_algorithm.cpp b/refcode/5-geometry/ccw_algorithm.cpp
similarity index 100%
rename from 5-geometry/ccw_algorithm.cpp
rename to refcode/5-geometry/ccw_algorithm.cpp
diff --git a/5-geometry/convex_hull.cpp b/refcode/5-geometry/convex_hull.cpp
similarity index 100%
rename from 5-geometry/convex_hull.cpp
rename to refcode/5-geometry/convex_hull.cpp
diff --git a/5-geometry/minimum_enclosing_circle.cpp b/refcode/5-geometry/minimum_enclosing_circle.cpp
similarity index 100%
rename from 5-geometry/minimum_enclosing_circle.cpp
rename to refcode/5-geometry/minimum_enclosing_circle.cpp
diff --git a/5-geometry/ray_casting.cpp b/refcode/5-geometry/ray_casting.cpp
similarity index 100%
rename from 5-geometry/ray_casting.cpp
rename to refcode/5-geometry/ray_casting.cpp
diff --git a/5-geometry/rotating_callipers.cpp b/refcode/5-geometry/rotating_callipers.cpp
similarity index 100%
rename from 5-geometry/rotating_callipers.cpp
rename to refcode/5-geometry/rotating_callipers.cpp
diff --git a/5-geometry/sort_by_angular.cpp b/refcode/5-geometry/sort_by_angular.cpp
similarity index 100%
rename from 5-geometry/sort_by_angular.cpp
rename to refcode/5-geometry/sort_by_angular.cpp
diff --git a/6-math/basic_sqrt_time_algorithms.cpp b/refcode/6-math/basic_sqrt_time_algorithms.cpp
similarity index 100%
rename from 6-math/basic_sqrt_time_algorithms.cpp
rename to refcode/6-math/basic_sqrt_time_algorithms.cpp
diff --git a/6-math/binomial_coefficient.cpp b/refcode/6-math/binomial_coefficient.cpp
similarity index 100%
rename from 6-math/binomial_coefficient.cpp
rename to refcode/6-math/binomial_coefficient.cpp
diff --git a/6-math/catalan_number_derangement_number.cpp b/refcode/6-math/catalan_number_derangement_number.cpp
similarity index 100%
rename from 6-math/catalan_number_derangement_number.cpp
rename to refcode/6-math/catalan_number_derangement_number.cpp
diff --git a/6-math/chinese_remainder_theorem.cpp b/refcode/6-math/chinese_remainder_theorem.cpp
similarity index 100%
rename from 6-math/chinese_remainder_theorem.cpp
rename to refcode/6-math/chinese_remainder_theorem.cpp
diff --git a/6-math/euclidean_algorithms.cpp b/refcode/6-math/euclidean_algorithms.cpp
similarity index 100%
rename from 6-math/euclidean_algorithms.cpp
rename to refcode/6-math/euclidean_algorithms.cpp
diff --git a/6-math/eulers_phi_function.cpp b/refcode/6-math/eulers_phi_function.cpp
similarity index 100%
rename from 6-math/eulers_phi_function.cpp
rename to refcode/6-math/eulers_phi_function.cpp
diff --git a/6-math/fft.cpp b/refcode/6-math/fft.cpp
similarity index 100%
rename from 6-math/fft.cpp
rename to refcode/6-math/fft.cpp
diff --git a/6-math/gauss_jordan_elimination.cpp b/refcode/6-math/gauss_jordan_elimination.cpp
similarity index 100%
rename from 6-math/gauss_jordan_elimination.cpp
rename to refcode/6-math/gauss_jordan_elimination.cpp
diff --git a/6-math/matrix.cpp b/refcode/6-math/matrix.cpp
similarity index 100%
rename from 6-math/matrix.cpp
rename to refcode/6-math/matrix.cpp
diff --git a/6-math/miller_rabin_pollard_rho.cpp b/refcode/6-math/miller_rabin_pollard_rho.cpp
similarity index 100%
rename from 6-math/miller_rabin_pollard_rho.cpp
rename to refcode/6-math/miller_rabin_pollard_rho.cpp
diff --git a/6-math/mobius.cpp b/refcode/6-math/mobius.cpp
similarity index 100%
rename from 6-math/mobius.cpp
rename to refcode/6-math/mobius.cpp
diff --git a/6-math/sieve.cpp b/refcode/6-math/sieve.cpp
similarity index 100%
rename from 6-math/sieve.cpp
rename to refcode/6-math/sieve.cpp
diff --git a/7-misc/dp_opt.cpp b/refcode/7-misc/dp_opt.cpp
similarity index 100%
rename from 7-misc/dp_opt.cpp
rename to refcode/7-misc/dp_opt.cpp
diff --git a/7-misc/fraction_data_type.cpp b/refcode/7-misc/fraction_data_type.cpp
similarity index 100%
rename from 7-misc/fraction_data_type.cpp
rename to refcode/7-misc/fraction_data_type.cpp
diff --git a/7-misc/kitamasa.cpp b/refcode/7-misc/kitamasa.cpp
similarity index 100%
rename from 7-misc/kitamasa.cpp
rename to refcode/7-misc/kitamasa.cpp
diff --git a/7-misc/lis_in_o_nlogn.cpp b/refcode/7-misc/lis_in_o_nlogn.cpp
similarity index 100%
rename from 7-misc/lis_in_o_nlogn.cpp
rename to refcode/7-misc/lis_in_o_nlogn.cpp
diff --git a/7-misc/random.cpp b/refcode/7-misc/random.cpp
similarity index 100%
rename from 7-misc/random.cpp
rename to refcode/7-misc/random.cpp
diff --git a/7-misc/rotation_matrix_manhattan_distance_chebyshev_distance.txt b/refcode/7-misc/rotation_matrix_manhattan_distance_chebyshev_distance.txt
similarity index 100%
rename from 7-misc/rotation_matrix_manhattan_distance_chebyshev_distance.txt
rename to refcode/7-misc/rotation_matrix_manhattan_distance_chebyshev_distance.txt
diff --git a/7-misc/simd.cpp b/refcode/7-misc/simd.cpp
similarity index 100%
rename from 7-misc/simd.cpp
rename to refcode/7-misc/simd.cpp
diff --git a/7-misc/sqrt_decomposition_mos_algorithm.cpp b/refcode/7-misc/sqrt_decomposition_mos_algorithm.cpp
similarity index 100%
rename from 7-misc/sqrt_decomposition_mos_algorithm.cpp
rename to refcode/7-misc/sqrt_decomposition_mos_algorithm.cpp
diff --git a/7-misc/system_of_difference_constraints.cpp b/refcode/7-misc/system_of_difference_constraints.cpp
similarity index 100%
rename from 7-misc/system_of_difference_constraints.cpp
rename to refcode/7-misc/system_of_difference_constraints.cpp
diff --git a/7-misc/ternary_search.cpp b/refcode/7-misc/ternary_search.cpp
similarity index 100%
rename from 7-misc/ternary_search.cpp
rename to refcode/7-misc/ternary_search.cpp
diff --git a/common/common.hpp b/refcode/common/common.hpp
similarity index 100%
rename from common/common.hpp
rename to refcode/common/common.hpp
index 3321f91..aa84e02 100644
--- a/common/common.hpp
+++ b/refcode/common/common.hpp
@@ -7,7 +7,7 @@ using ll = long long;
 using pii = pair<int, int>;
 using pll = pair<ll, ll>;
 
-#define sz(x) (int)(x).size()
-#define all(x) (x).begin(), (x).end()
 #define fr first
 #define sc second
+#define sz(x) (int)(x).size()
+#define all(x) (x).begin(), (x).end()
diff --git a/test/.gitkeep b/test/.gitkeep
new file mode 100644
index 0000000..e69de29