diff --git a/.DS_Store b/.DS_Store
index 263b422c..1954b2ec 100644
Binary files a/.DS_Store and b/.DS_Store differ
diff --git a/.github/workflows/macos_test_cases.yml b/.github/workflows/macos_test_cases.yml
index 4c88fe47..9f7bc219 100644
--- a/.github/workflows/macos_test_cases.yml
+++ b/.github/workflows/macos_test_cases.yml
@@ -42,7 +42,7 @@ jobs:
         # See https://cmake.org/cmake/help/latest/manual/ctest.1.html for more detail
         run: ctest --output-on-failure
       - name: Upload coverage reports to Codecov
-        uses: codecov/codecov-action@v4.6.0
+        uses: codecov/codecov-action@v5.0.2
         with:
           token: ${{ secrets.CODECOV_TOKEN }}
           slug: CSRT-NTUA/AlgoPlus
diff --git a/src/algorithms/dynamic_programming/knapsack.h b/src/algorithms/dynamic_programming/knapsack.h
new file mode 100644
index 00000000..391c3edb
--- /dev/null
+++ b/src/algorithms/dynamic_programming/knapsack.h
@@ -0,0 +1,39 @@
+#ifndef KNAPSACK_H
+#define KNAPSACK_H
+
+#ifdef __cplusplus
+#include <iostream>
+#include <vector>
+#include <utility>
+#endif
+
+/**
+* @brief knapsack 0/1 function
+* @param v the passed vector
+* @param capacity the capacity of the knapsack
+* @return int: the maximum value you can collect with a knapsack of the passed capacity
+*/
+int knapsack(std::vector<std::pair<int, int> > &v, int capacity) {
+    if(capacity == 0) {
+        return 0;
+    }
+
+    int n = int(v.size());
+    std::vector<std::vector<int > > dp(n + 1, std::vector<int>(capacity + 1));
+
+    for(int i = 1; i<=n; i++) {
+        for(int j = 0; j<=capacity; j++) {
+            dp[i][j] = dp[i - 1][j];
+            if(i == 0 || j == 0) {
+                dp[i][j] = 0;
+            }
+            else if(v[i - 1].first <= j) {
+                dp[i][j] = std::max(dp[i - 1][j], v[i - 1].second + dp[i - 1][j - v[i - 1].first]);
+            }
+        }
+    }
+
+    return dp[n][capacity];
+}
+
+#endif
diff --git a/src/algorithms/dynamic_programming/subset_sum.h b/src/algorithms/dynamic_programming/subset_sum.h
new file mode 100644
index 00000000..f8e85082
--- /dev/null
+++ b/src/algorithms/dynamic_programming/subset_sum.h
@@ -0,0 +1,40 @@
+#ifndef SUBSET_SUM_H
+#define SUBSET_SUM_H
+
+#ifdef __cplusplus
+#include <iostream>
+#include <vector>
+#include <cassert>
+#endif
+
+/**
+* @brief subset sum function
+* @details Returns the number of subsets you can create with sum of B
+* @param v: the passed vector
+* @param B: the sum
+* @returns: int, the total number of subsets you can create
+*/
+int subset_sum(std::vector<int> &v, int B) {
+    if(int(v.size()) == 0) {
+        return 0;
+    }
+    int n = int(v.size());
+    std::vector<std::vector<int> > dp(n + 1, std::vector<int>(B + 1, 0));
+    for(int i = 0; i<=n; i++) {
+        dp[i][0] = 1;
+    }
+
+    for(int i = 1; i<=n; i++) {
+        for(int j = 0; j<=B; j++) {
+            dp[i][j] = dp[i - 1][j];
+
+            if(j - v[i - 1] >= 0) {
+                dp[i][j] += dp[i - 1][j - v[i - 1]];
+            }
+        }
+    }
+
+    return dp[n][B];
+}
+
+#endif
diff --git a/src/classes/tree/avl_tree.h b/src/classes/tree/avl_tree.h
index 875da11c..69d613c2 100644
--- a/src/classes/tree/avl_tree.h
+++ b/src/classes/tree/avl_tree.h
@@ -211,7 +211,7 @@ template <typename T> class avl_tree {
    * @brief operator << for avl_tree class
    */
   friend std::ostream & operator << (std::ostream &out, avl_tree<T> &t){
-    std::vector<std::vector<T> > order = t.inorder();
+    std::vector<T> order = t.inorder();
     for(int i = 0; i<order.size(); i++){
       if(i != order.size() - 1){
         out << order[i] << ", ";
diff --git a/src/classes/tree/bst.h b/src/classes/tree/bst.h
index aa308f11..063dffac 100644
--- a/src/classes/tree/bst.h
+++ b/src/classes/tree/bst.h
@@ -200,7 +200,7 @@ template <typename T> class bst {
    * @brief operator << for bst class
    */
   friend std::ostream & operator << (std::ostream &out, bst<T> &t){
-    std::vector<std::vector<T> > order = t.inorder();
+    std::vector<T> order = t.inorder();
     for(int i = 0; i<order.size(); i++){
       if(i != order.size() - 1){
         out << order[i] << ", ";
diff --git a/src/classes/tree/splay_tree.h b/src/classes/tree/splay_tree.h
index 2e9682cd..bcfa0095 100644
--- a/src/classes/tree/splay_tree.h
+++ b/src/classes/tree/splay_tree.h
@@ -213,7 +213,7 @@ template <typename T> class splay_tree {
    * @brief operator << for splay tree class
    */
   friend std::ostream & operator << (std::ostream &out, splay_tree<T> &t){
-    std::vector<std::vector<T> > order = t.inorder();
+    std::vector<T> order = t.inorder();
     for(int i = 0; i<order.size(); i++){
       if(i != order.size() - 1){
         out << order[i] << ", ";
diff --git a/src/classes/tree/tree.h b/src/classes/tree/tree.h
index ab8eb8d0..86657664 100644
--- a/src/classes/tree/tree.h
+++ b/src/classes/tree/tree.h
@@ -186,7 +186,7 @@ template <typename T> class tree {
    * @brief operator << for bst class
    */
   friend std::ostream & operator << (std::ostream &out, tree<T> &t){
-    std::vector<std::vector<T> > order = t.inorder();
+    std::vector<T> order = t.inorder();
     for(int i = 0; i<order.size(); i++){
       if(i != order.size() - 1){
         out << order[i] << ", ";
diff --git a/src/machine_learning/regression/linear_regression/lin_reg.h b/src/machine_learning/regression/linear_regression/lin_reg.h
index ef05056e..ad92320e 100644
--- a/src/machine_learning/regression/linear_regression/lin_reg.h
+++ b/src/machine_learning/regression/linear_regression/lin_reg.h
@@ -20,7 +20,7 @@ class linear_regression{
   double Sxy, Sxx;
   double x_mean, y_mean;
 public:
-  
+
   /**
   * @brief Constructor for linear regression class
   * @param points: 2D points that user pass to the regressor
@@ -41,7 +41,7 @@ class linear_regression{
       std::cerr << e.what() << '\n';
     }
   }
-  
+
   /**
   * @brief get_results function
   * @return pair<double,double> the values of a and b
diff --git a/tests/algorithms/dynamic_programming/knapsack.cc b/tests/algorithms/dynamic_programming/knapsack.cc
new file mode 100644
index 00000000..6136ef1b
--- /dev/null
+++ b/tests/algorithms/dynamic_programming/knapsack.cc
@@ -0,0 +1,12 @@
+#include "../../../third_party/catch.hpp"
+#include "../../../src/algorithms/dynamic_programming/knapsack.h"
+
+TEST_CASE("Testing knapsack 0/1 [1]") {
+    std::vector<std::pair<int, int> > v = {{10, 60}, {20, 100}, {30, 120}};
+
+    REQUIRE(knapsack(v, 50) == 220);
+    v.clear();
+    v = {{5, 40}, {3, 20}, {6, 10}, {3, 30}};
+
+    REQUIRE(knapsack(v, 10) == 70);
+}
diff --git a/tests/algorithms/dynamic_programming/subset_sum.cc b/tests/algorithms/dynamic_programming/subset_sum.cc
new file mode 100644
index 00000000..9fac4143
--- /dev/null
+++ b/tests/algorithms/dynamic_programming/subset_sum.cc
@@ -0,0 +1,23 @@
+#include "../../../third_party/catch.hpp"
+#include "../../../src/algorithms/dynamic_programming/subset_sum.h"
+
+TEST_CASE("Testing subset sum [1]") {
+    std::vector<int> v {4, 2, 1, 5, 7};
+    int B = 7;
+
+    REQUIRE(subset_sum(v, B) == 3);
+    v.clear();
+
+    REQUIRE(subset_sum(v, B) == 0);
+}
+
+TEST_CASE("Testing subset sum [2]") {
+    std::vector<int> v {1, 4, 6, 9};
+    int B = 5;
+
+    REQUIRE(subset_sum(v, B) == 1);
+    B = 6;
+    REQUIRE(subset_sum(v, 6) == 1);
+    B = 9;
+    REQUIRE(subset_sum(v, B) == 1);
+}
diff --git a/tests/tree/avl.cc b/tests/tree/avl.cc
index 1752d9fa..8ead82d6 100644
--- a/tests/tree/avl.cc
+++ b/tests/tree/avl.cc
@@ -164,6 +164,14 @@ TEST_CASE("Testing get_root function in avl tree"){
   REQUIRE(t.get_root() == 36);
 }
 
+TEST_CASE("Testing operator << for avl tree") {
+    avl_tree<int> t({1, 10, 2, 8, 6, 5});
+    REQUIRE_NOTHROW(cout << t);
+
+    avl_tree<char> tt({'a', 'g', 'd', 'z', 'w', 'f'});
+    REQUIRE_NOTHROW(cout << tt);
+}
+
 #define TREE_VISUALIZATION_H
 #ifdef TREE_VISUALIZATION_H
 
diff --git a/tests/tree/bst.cc b/tests/tree/bst.cc
index 9a260aa2..830b3e50 100644
--- a/tests/tree/bst.cc
+++ b/tests/tree/bst.cc
@@ -151,6 +151,14 @@ TEST_CASE("testing level order in bst"){
   REQUIRE(produced == sol);
 }
 
+TEST_CASE("Testing opearator << for bst") {
+    bst<int> t({1, 10, 5, 3, 9, 25});
+    REQUIRE_NOTHROW(cout << t);
+
+    bst<char> tt({'a', 'g', 'q', 'v', 'w'});
+    REQUIRE_NOTHROW(cout << tt);
+}
+
 #define TREE_VISUALIZATION_H
 #ifdef TREE_VISUALIZATION_H
 
diff --git a/tests/tree/splay_tree.cc b/tests/tree/splay_tree.cc
index 04e2926e..01b8a754 100644
--- a/tests/tree/splay_tree.cc
+++ b/tests/tree/splay_tree.cc
@@ -128,6 +128,14 @@ TEST_CASE("testing level order for splay tree"){
   REQUIRE(produced==sol);
 }
 
+TEST_CASE("Testing operator << for splay tree") {
+    splay_tree<int> t({1, 5, 3, 2, 9, 11});
+    REQUIRE_NOTHROW(cout << t);
+
+    splay_tree<char> tt({'a', 'b', 'w', 'z', 'f', 'd'});
+    REQUIRE_NOTHROW(cout << tt);
+}
+
 #define TREE_VISUALIZATION_H
 #ifdef TREE_VISUALIZATION_H
 
diff --git a/tests/tree/tree.cc b/tests/tree/tree.cc
index d0de6f33..138888f4 100644
--- a/tests/tree/tree.cc
+++ b/tests/tree/tree.cc
@@ -53,6 +53,27 @@ TEST_CASE("testing level order traversal in tree class [TREECLASS]"){
   REQUIRE(produced == sol);
 }
 
+TEST_CASE("Testing operator << for tree") {
+    tree<int> t;
+    t.insert("", 1);
+    t.insert("l", 2);
+    t.insert("r", 3);
+    t.insert("ll", 4);
+    t.insert("lr", 5);
+    t.insert("rl", 6);
+    t.insert("rr", 7);
+    t.insert("lll", 8);
+    t.insert("llr", 9);
+    t.insert("lrl", 10);
+    REQUIRE_NOTHROW(cout << t);
+
+    tree<std::string> tt;
+    tt.insert("", "hello");
+    tt.insert("r", "world");
+    tt.insert("l", "universe");
+    REQUIRE_NOTHROW(cout << tt);
+}
+
 #define TREE_VISUALIZATION_H
 #ifdef TREE_VISUALIZATION_H