Create Balanced-Binary-Tree.java and Updated README.md (#148)

* README file with Balanced-Binary-Tree problem

* create Balanced-Binary-Tree.java

Author: sujin0529

Java/Balanced-Binary-Tree.java

@@ -0,0 +1,46 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode() {}
+ *     TreeNode(int val) { this.val = val; }
+ *     TreeNode(int val, TreeNode left, TreeNode right) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+class Solution {
+    public boolean isBalanced(TreeNode root) {
+        
+        if(root==null){
+            return true;
+        }
+        else{
+            int left = height(root.left);
+            int right = height(root.right);
+            int diff = left - right;
+            diff = diff > 0 ? diff : -diff; // absolute
+            if(diff > 1){
+                return false;
+            }
+            return isBalanced(root.left) && isBalanced(root.right);
+        }
+    }
+    
+    private int height(TreeNode root){
+        // calculate the height of a tree
+        if(root == null){
+            return 0;
+        }
+        else{
+            int left = height(root.left);
+            int right = height(root.right);
+            int height = left > right ? left : right;
+            return height + 1;
+        }
+    }
+}

README.md

@@ -330,6 +330,7 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 | 1463 | [Cherry Pickup II](https://leetcode.com/problems/cherry-pickup-ii/)                         | [C++](./C++/Cherry-Pickup-II.cpp)                  | _O(n \* m)_ | _O(n \* m)_ | Hard       | DFS |      |
 | 104  | [Maximum Depth of Binary Tree](https://leetcode.com/problems/maximum-depth-of-binary-tree/) | [python](./Python/maximum-depth-of-binary-tree.py) | _O(n)_      | _O(n)_      | Easy       | DFS |      |
 | 112 | [Path Sum](https://leetcode.com/problems/path-sum/) | [Java](./Java/path-sum.java) | _O(n)_ | _O(n)_ | Easy | DFS |     |
+| 110 | [Balanced Binary Tree](https://leetcode.com/problems/balanced-binary-tree/) | [Java](./Java/Balanced-Binary-Tree.java) | _O(n)_ | _O(n)_ | Easy | DFS |     |
 
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