Added level order traversal in Binary trees (#153)

* 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

@@ -3,3 +3,4 @@
 ### C or C++
 
 1. [Pre, In & Post Order Traversals](c-or-cpp/pre-in-post-traversal.cpp)
+2. [Level Order Traversal](c-or-cpp/level-order-traversal.cpp)

trees/c-or-cpp/level-order-traversal.cpp

@@ -0,0 +1,74 @@
+#include<iostream>
+#include<queue>
+#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;
+    }
+};
+
+/* Level order Traversal of a Binary Tree using Queue */
+/* Complexity : O(n) */
+
+// Here NULLs are used to keep track of levels
+
+void level_order(Node* root){
+    if(root == NULL) 
+     return;
+
+    queue<Node*> q;
+    q.push(root); q.push(NULL);
+
+    while(!q.empty()){
+        Node* node = q.front();
+        q.pop();
+        
+        if(node != NULL){
+            cout<<node->data<<" ";
+            if(node->left)
+                q.push(node->left);
+            
+            if(node->right)
+                q.push(node->right);
+            
+        }else if(!q.empty()){
+            q.push(NULL);
+        }
+    }
+    cout<<endl;
+}
+
+
+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-> level-order :  1,2,3,4,5,7
+                   
+    
+    */
+   cout<<"Level Order is : ";
+   level_order(root);
+
+    return 0;
+}