Added 3 basic traversals in Binary Trees (#144)

* added max subarray sum

* added pre,in,post traversals

* Update pre-in-post-traversal.cpp

formatted the output

* Update pre-in-post-traversal.cpp

formatted output

Co-authored-by: Arsenic <54987647+Arsenic-ATG@users.noreply.github.com>

trees/README.md

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+# Trees
+
+### C or C++
+
+1. [Pre, In & Post Order Traversals](c-or-cpp/pre-in-post-traversal.cpp)

trees/c-or-cpp/pre-in-post-traversal.cpp

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+#include<iostream>
+#define endl "\n"
+using namespace std;
+
+
+// Basic Structure of a Tree
+struct Node{
+    int data;
+    struct Node *left;
+    struct Node *right;
+
+    Node(int val){
+        data = val;
+        left = NULL;
+        right = NULL;
+    }
+};
+
+/* Pre, In and Post order Traversal of a Binary Tree using recusrion */
+/* Complexity for each Traversal : O(n) */
+
+// LST -> Left SubTree   RST -> Right SubTree
+
+// Pre-Order goes like :-   Root, LST, RST (Recursively)
+void pre_order(struct Node* root){
+    if(root == NULL)
+      return;
+    cout<<root->data<<" ";
+    pre_order(root->left);
+    pre_order(root->right);
+}
+
+// In-Order goes like :-   LST, Root, RST (Recursively)
+void in_order(struct Node* root){
+    if(root == NULL)
+      return;
+    in_order(root->left);
+    cout<<root->data<<" ";
+    in_order(root->right);
+}
+
+// Pre-Order goes like :-  LST, RST, Root (Recursively)
+void post_order(struct Node* root){
+    if(root == NULL)
+      return;
+    post_order(root->left);
+    post_order(root->right);
+    cout<<root->data<<" ";
+}
+
+
+int main(){
+    Node* root = new Node(1);
+    root->left = new Node(2);
+    root->right = new Node(3);
+    root->left->left = new Node(4);
+    root->left->right = new Node(5);
+    root->right->right = new Node(7);
+
+    /*                       
+                    1
+                   / \
+                  2   3
+                 / \   \
+                4   5   7    
+        Expected-> pre-order :  1,2,4,5,3,7
+                   in-order  :  4,2,5,1,3,7
+                   post-order:  4,5,2,7,3,1
+    
+    */
+   cout<<"pre-order : "; pre_order(root); cout<<endl;
+   cout<<"in-order : "; in_order(root); cout<<endl;
+   cout<<"post-order : "; post_order(root); cout<<endl;
+
+    return 0;
+}