java: add «1367. Linked List in Binary Tree»

Signed-off-by: Matej Focko <me@mfocko.xyz>

java/ListNode.java

@@ -0,0 +1,15 @@
+public class ListNode {
+  int val;
+  ListNode next;
+
+  ListNode() {}
+
+  ListNode(int val) {
+    this.val = val;
+  }
+
+  ListNode(int val, ListNode next) {
+    this.val = val;
+    this.next = next;
+  }
+}

java/linked-list-in-binary-tree.java

@@ -0,0 +1,37 @@
+class Solution {
+  private boolean matches(ListNode head, TreeNode node) {
+    // linked list ran out ⇒ matches
+    if (head == null) {
+      return true;
+    }
+
+    // ran out of tree nodes ⇒ failed
+    if (node == null) {
+      return false;
+    }
+
+    // values don't match ⇒ failed
+    if (head.val != node.val) {
+      return false;
+    }
+
+    // check rest of the path
+    return matches(head.next, node.left) || matches(head.next, node.right);
+  }
+
+  public boolean isSubPath(ListNode head, TreeNode node) {
+    // cannot form a subpath
+    if (node == null) {
+      return false;
+    }
+
+    // check path starting from the current node
+    var result = matches(head, node);
+
+    // if doesn't match linked list, try from subtrees
+    result = result || isSubPath(head, node.left);
+    result = result || isSubPath(head, node.right);
+
+    return result;
+  }
+}