diff --git a/algorithm/graph_algorithm.cpp b/algorithm/graph_algorithm.cpp
new file mode 100644
index 0000000..6630fd2
--- /dev/null
+++ b/algorithm/graph_algorithm.cpp
@@ -0,0 +1,48 @@
+#include <iostream>
+#include <list>
+#include <vector>
+#include <queue>
+
+template<class T>
+struct graph {
+public:
+  graph(int v_num):v(v_num) {
+    edge = std::vector<std::list<T>>(v_num);
+    indegree = std::vector<int>(v_num, 0);
+  }
+
+  void addEdge(int from, int to) {
+    edge[in].push_back(to);
+    indegree[to]++;
+  }
+
+  int v;
+  vector<int> indegree;
+  std::vector<list<T>> edge;
+
+}
+
+template<class T>
+void topological_sorting(graph<T> g) {
+  std::queue<int> q;
+
+  for (int i = 0; i < g.indegree.size(); ++i ) {
+    if (g.indegree[i] == 0) {
+      q.push[i];
+    }
+  }
+
+  while(!q.empty()) {
+    int v = q.top()
+    std::cout << v << std::endl;
+    q.pop();
+    for (auto i = g.edge[v].begin(); i != g.edge[v].end(), ++i) {
+      g.indegree[*i]--;
+      if (g.indegree[*i] == 0) q.push(*i);
+    }
+  }
+  return;
+}
+
+int main() {
+}
diff --git a/algorithm/tree_algorithms.cpp b/algorithm/tree_algorithms.cpp
new file mode 100644
index 0000000..d9dac5c
--- /dev/null
+++ b/algorithm/tree_algorithms.cpp
@@ -0,0 +1,105 @@
+#include <iostream>
+#include <vector>
+#include <stack>
+
+template<class T>
+struct node {
+public:
+  node():left(nullptr), right(nullptr) {}
+  T value;
+  node * left;
+  node * right;
+};
+
+template<class T>
+void DLR(node<T> * root) {
+  std::stack<node<T> *> stack;
+  stack.push(root);
+
+  node<T> * top;
+  while(!stack.empty()) {
+    top = stack.top();
+    std::cout << top->value << std::endl;
+    stack.pop();
+    if (top->right != nullptr) stack.push(top->right);
+    if (top->left != nullptr) stack.push(top->left);
+  }
+  return;
+};
+
+template<class T>
+void LDR(node<T> * root) {
+  std::stack<node<T> *> stack;
+  while(root != nullptr || !stack.empty()) {
+    while(root != nullptr) {
+      stack.push(root);
+      root = root->left;
+    }
+    if(!stack.empty()){
+      root = stack.top();
+      std::cout << root->value << std::endl;
+      stack.pop();
+      root = root->right;
+    }
+  }
+  return;
+};
+
+template<class T>
+void LRD(node<T> * root) {
+  if (root == nullptr) return;
+  std::stack<node<T> *> stack;
+  stack.push(root);
+
+  node<T> * last_pop = nullptr;
+  while(!stack.empty()) {
+    while(root->left != nullptr) {
+      root = root->left;
+      stack.push(root);
+    }
+    while(!stack.empty()) {
+      if (root->right == nullptr || root->right == last_pop) {
+        std::cout << root->value << std::endl;
+        stack.pop();
+        last_pop = root;
+        if (!stack.empty()){
+          root = stack.top();
+        }
+      } else {
+        root = root->right;
+        stack.push(root);
+        break;
+      }
+    }
+  }
+  return;
+};
+
+/*
+        1
+       / \
+      2   3
+       \
+        4
+       /
+      5
+*/
+
+int main() {
+  node<int> * root = new node<int>();
+  root->value = 1;
+  root->left = new node<int>();
+  root->left->value = 2;
+  root->right = new node<int>();
+  root->right->value = 3;
+  root->left->right = new node<int>();
+  root->left->right->value = 4;
+  root->left->right->left = new node<int>();
+  root->left->right->left->value = 5;
+
+  DLR(root);
+  LDR(root);
+  LRD(root);
+
+  return 0;
+}