solves #114 in java

Author: anishLearnsToCode

README.md

@@ -106,7 +106,7 @@
 | 111  | [Minimum Depth of Binary Tree](https://leetcode.com/problems/minimum-depth-of-binary-tree)                                                                |                         [![Java](assets/java.png)](src/MinimumDepthOfBinaryTree.java) [![Python](assets/python.png)](python/minimum_depth_of_binary_tree.py)                         |                                                                                                                                   |
 | 112  | [Path Sum](https://leetcode.com/problems/path-sum)                                                                                                        |                                           [![Java](assets/java.png)](src/PathSum.java) [![Python](assets/python.png)](python/path_sum.py)                                            |                                                                                                                                   |
 | 113  | [Path Sum II](https://leetcode.com/problems/path-sum-ii)                                                                                                  |                                                                    [![Java](assets/java.png)](src/PathSumII.java)                                                                    |                                                                                                                                   |
-| 114  | [Flatten Binary Tree to Linked List](https://leetcode.com/problems/flatten-binary-tree-to-linked-list)                                                    |                                                                                                                                                                                      |                                                                                                                                   |
+| 114  | [Flatten Binary Tree to Linked List](https://leetcode.com/problems/flatten-binary-tree-to-linked-list)                                                    |                                                          [![Java](assets/java.png)](src/FlattenBinaryTreeToLinkedList.java)                                                          |                                                                                                                                   |
 | 116  | [Populating Next Right Pointers in Each Node](https://leetcode.com/problems/populating-next-right-pointers-in-each-node)                                  |                                                                                                                                                                                      |                                                                                                                                   |
 | 117  | [Populating Next Right Pointers in Each Node II](https://leetcode.com/problems/populating-next-right-pointers-in-each-node-ii)                            |                                                                                                                                                                                      |                                                                                                                                   |
 | 118  | [Pascal's Triangle](https://leetcode.com/problems/pascals-triangle)                                                                                       |                                   [![Java](assets/java.png)](src/PascalsTriangle.java) [![Python](assets/python.png)](python/pascals_triangle.py)                                    |                                                                                                                                   |

src/FlattenBinaryTreeToLinkedList.java

@@ -0,0 +1,26 @@
+// https://leetcode.com/problems/flatten-binary-tree-to-linked-list
+// T: O(n)
+// S: O(log(n))
+
+public class FlattenBinaryTreeToLinkedList {
+    public static void flatten(TreeNode root) {
+        flattenAndGetLastNode(root);
+    }
+
+    private static TreeNode flattenAndGetLastNode(TreeNode root) {
+        if (root == null) return null;
+
+        TreeNode leftLast = flattenAndGetLastNode(root.left);
+        TreeNode rightLast = flattenAndGetLastNode(root.right);
+
+        if (root.left != null) {
+            leftLast.right = root.right;
+            root.right = root.left;
+            root.left = null;
+        }
+
+        return rightLast != null
+                ? rightLast
+                : (leftLast == null ? root : leftLast);
+    }
+}

src/HelloWorld.java

@@ -1,23 +1,17 @@
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.List;
-
 public class HelloWorld {
     public static void main(String[] args) {
-//        ConstructBinaryTreeFromInorderAndPostorderTraversal c = new ConstructBinaryTreeFromInorderAndPostorderTraversal();
-//        TreeNode treeNode = c.buildTree(new int[] {9, 3, 15, 20, 7}, new int[] {9, 15, 7, 20, 3});
-//        TreePrinter.print(treeNode);
-//
-//        c = new ConstructBinaryTreeFromInorderAndPostorderTraversal();
-//        treeNode = c.buildTree(new int[] {2, 1}, new int[] {2, 1});
-//        TreePrinter.print(treeNode);
-//
-//        c = new ConstructBinaryTreeFromInorderAndPostorderTraversal();
-//        treeNode = c.buildTree(new int[] {-1}, new int[] {-1});
-//        TreePrinter.print(treeNode);
+        TreeNode root = new TreeNode(1);
+        root.left = new TreeNode(2);
+        root.right = new TreeNode(5);
+        root.left.left = new TreeNode(3);
+        root.left.right = new TreeNode(4);
+        root.right.right = new TreeNode(6);
+
+        TreePrinter.print(root);
+
+        FlattenBinaryTreeToLinkedList.flatten(root);
+
+        TreePrinter.print(root);
 
-        ConstructBinaryTreeFromInorderAndPostorderTraversal c = new ConstructBinaryTreeFromInorderAndPostorderTraversal();
-        TreeNode treeNode = c.buildTree(new int[] {1, 2, 3, 4}, new int[] {2, 1, 3, 4});
-        TreePrinter.print(treeNode);
     }
 }

src/TreeNode.java

@@ -3,13 +3,24 @@ public class TreeNode implements TreePrinter.PrintableNode {
     TreeNode left;
     TreeNode right;
     TreeNode() {}
-    TreeNode(int val) { this.val = val; }
+
+    TreeNode(int val) {
+        this.val = val;
+    }
+
     TreeNode(int val, TreeNode left, TreeNode right) {
         this.val = val;
         this.left = left;
         this.right = right;
     }
 
+    @Override
+    public String toString() {
+        return "TreeNode{" +
+                "val=" + val +
+                '}';
+    }
+
     @Override
     public TreePrinter.PrintableNode getLeft() {
         return this.left;