From 33e47203c69b6807344d8845070f6becbe8ed560 Mon Sep 17 00:00:00 2001
From: Matej Focko <me@mfocko.xyz>
Date: Tue, 16 Jul 2024 23:29:42 +0200
Subject: [PATCH] =?UTF-8?q?java:=20add=20=C2=AB2096.=20Step-By-Step=20Dire?=
 =?UTF-8?q?ctions=20From=20a=20Binary=20Tree=20Node=20to=20Another=C2=BB?=
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Signed-off-by: Matej Focko <me@mfocko.xyz>
---
 ...ns-from-a-binary-tree-node-to-another.java | 70 +++++++++++++++++++
 1 file changed, 70 insertions(+)
 create mode 100644 java/step-by-step-directions-from-a-binary-tree-node-to-another.java

diff --git a/java/step-by-step-directions-from-a-binary-tree-node-to-another.java b/java/step-by-step-directions-from-a-binary-tree-node-to-another.java
new file mode 100644
index 0000000..57d6191
--- /dev/null
+++ b/java/step-by-step-directions-from-a-binary-tree-node-to-another.java
@@ -0,0 +1,70 @@
+class Solution {
+  private TreeNode getLowestCommonAncestor(TreeNode node, int key1, int key2) {
+    if (node == null) {
+      return null;
+    }
+
+    if (node.val == key1 || node.val == key2) {
+      return node;
+    }
+
+    var left = getLowestCommonAncestor(node.left, key1, key2);
+    var right = getLowestCommonAncestor(node.right, key1, key2);
+
+    if (left == null) {
+      return right;
+    }
+
+    if (right == null) {
+      return left;
+    }
+
+    return node;
+  }
+
+  private record Path(boolean found, StringBuilder path) {}
+
+  private Path getPath(TreeNode node, int key, StringBuilder path) {
+    if (node == null) {
+      return new Path(false, path);
+    }
+
+    if (node.val == key) {
+      return new Path(true, path);
+    }
+
+    // go left
+    path.append('L');
+    var leftPath = getPath(node.left, key, path);
+    if (leftPath.found) {
+      return leftPath;
+    }
+    path.deleteCharAt(path.length() - 1);
+
+    // go right
+    path.append('R');
+    var rightPath = getPath(node.right, key, path);
+    if (rightPath.found) {
+      return rightPath;
+    }
+    path.deleteCharAt(path.length() - 1);
+
+    return new Path(false, path);
+  }
+
+  public String getDirections(TreeNode root, int startValue, int destValue) {
+    var commonAncestor = getLowestCommonAncestor(root, startValue, destValue);
+    var pathToStart = getPath(commonAncestor, startValue, new StringBuilder());
+    var pathToDest = getPath(commonAncestor, destValue, new StringBuilder());
+
+    var directions = new StringBuilder();
+
+    // gotta go up from the start
+    directions.repeat('U', pathToStart.path.length());
+
+    // and then follow the directions down
+    directions.append(pathToDest.path);
+
+    return directions.toString();
+  }
+}