Issue #194--Added : 102. Binary Tree Level Order Traversal (#198)

* Added : 102. Binary Tree Level Order Traversal

* Update README.md

Author: pratik1424

C++/Binary-Tree-Level-Order-Traversal.cpp

@@ -0,0 +1,61 @@
+/*
+Problem:
+Given the root of a binary tree, return the level order traversal of its nodes' values. (i.e., from left to right, level by level).
+
+Example 1:
+Input: root = [3,9,20,null,null,15,7]
+Output: [[3],[9,20],[15,7]]
+
+Example 2:
+Input: root = [1]
+Output: [[1]]
+
+Example 3:
+Input: root = []
+Output: []
+ 
+Constraints:
+The number of nodes in the tree is in the range [0, 2000].
+-1000 <= Node.val <= 1000
+*/
+
+
+/*
+Space Complexity : O(N)
+Time Complexity : O(N)
+Difficulty level : Medium
+*/
+
+class Solution {
+public:
+	void fun( map<int,vector<int>>&mp, TreeNode* root, int level)
+{
+    if(!root)
+        return;
+    
+    mp[level].push_back(root->val);
+    
+    fun(mp,root->left,level+1);
+    fun(mp,root->right,level+1);
+    
+}
+
+    vector<vector<int>> levelOrder(TreeNode* root) {
+        vector<vector<int>>v;
+        if(!root)
+            return v;
+        
+        map<int,vector<int>>mp;
+        int level=0;
+        fun(mp,root,level);
+        auto it=mp.begin();
+        while(it!=mp.end())
+        {
+            v.push_back(it->second);  
+            it++;
+        }
+        
+        return v;
+        
+    }
+};

README.md

@@ -254,6 +254,7 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 | 968  | [Binary Tree Cameras](https://leetcode.com/problems/binary-tree-cameras/)                                       | [C++](./C++/Binary-Tree-Cameras.cpp)                                                                             | _O(n)_      | _O(logn)_   | Hard       | Binary Tree, Dynamic Programming               |
 | 98   | [Validate Binary Search Tree](https://leetcode.com/problems/validate-binary-search-tree/)                       | [Javascript](./JavaScript/98.Validate-Binary-Search-Tree.js)                                                     | _O(log(n))_ | _O(log(n))_ | Medium     | Binary Tree                                    |
 | 684  | [Redundant Connection](https://leetcode.com/problems/redundant-connection/)                                     | [Java](./Java/Redundant-Connection/redundant-connection.java)                                                    | _O(N)_      | _O(N)_      | Medium     | Tree, Union Find                               |
+| 102 | [Binary Tree Level Order Traversal](https://leetcode.com/problems/binary-tree-level-order-traversal/)   |[C++](./C++/Binary-Tree-Level-Order-Traversal.cpp)| _O(n)_      | _O(n)_      | Medium     | Binary Tree, map                                    |      |
 
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