add 114

Author: awesomelike

medium/114-flatten-binary-tree.java

@@ -0,0 +1,14 @@
+class Solution {
+  private TreeNode prev = null;
+
+  public void flatten(TreeNode root) {
+    if (root == null) {
+      return;
+    }
+    flatten(root.right);
+    flatten(root.left);  
+    root.right = prev;
+    root.left = null;
+    prev = root;
+  }
+}