java: add «2196. Create Binary Tree From Descriptions»

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

java/create-binary-tree-from-descriptions.java

@@ -0,0 +1,31 @@
+class Solution {
+  public TreeNode createBinaryTree(int[][] descriptions) {
+    Map<Integer, TreeNode> nodes = new HashMap<>();
+
+    Set<Integer> hasParent = new HashSet<>();
+    for (int[] description : descriptions) {
+      int parent = description[0];
+      int value = description[1];
+      boolean isLeft = description[2] == 1;
+
+      var parentNode = nodes.computeIfAbsent(parent, k -> new TreeNode(k));
+      var node = nodes.computeIfAbsent(value, k -> new TreeNode(k));
+
+      if (isLeft) {
+        parentNode.left = node;
+      } else {
+        parentNode.right = node;
+      }
+
+      hasParent.add(value);
+    }
+
+    for (var node : nodes.values()) {
+      if (!hasParent.contains(node.val)) {
+        return node;
+      }
+    }
+
+    return null;
+  }
+}