Solution.java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public TreeNode createBinaryTree(int[][] descriptions) {
        Map<Integer, TreeNode> nodes = new HashMap<>();
        Set<Integer> children = new HashSet<>();
        for (var d : descriptions) {
            int parent = d[0], child = d[1], isLeft = d[2];
            if (!nodes.containsKey(parent)) {
                nodes.put(parent, new TreeNode(parent));
            }
            if (!nodes.containsKey(child)) {
                nodes.put(child, new TreeNode(child));
            }
            if (isLeft == 1) {
                nodes.get(parent).left = nodes.get(child);
            } else {
                nodes.get(parent).right = nodes.get(child);
            }
            children.add(child);
        }
        for (var e : nodes.entrySet()) {
            if (!children.contains(e.getKey())) {
                return e.getValue();
            }
        }
        return null;
    }
}