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Java-based LeetCode algorithm problem solutions, regularly updated
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package g2101_2200.s2196_create_binary_tree_from_descriptions;

// #Medium #Array #Hash_Table #Depth_First_Search #Breadth_First_Search #Tree #Binary_Tree
// #2022_06_06_Time_85_ms_(76.70%)_Space_120.3_MB_(19.49%)

import com_github_leetcode.TreeNode;
import java.util.HashMap;
import java.util.Map;

/*
 * 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;
 *     }
 * }
 */
/**
 * 2196 - Create Binary Tree From Descriptions\.
 *
 * Medium
 *
 * You are given a 2D integer array `descriptions` where descriptions[i] = [parent_i, child_i, isLeft_i] indicates that parent_i is the **parent** of child_i in a **binary** tree of **unique** values. Furthermore,
 *
 * *   If isLeft_i == 1, then child_i is the left child of parent_i.
 * *   If isLeft_i == 0, then child_i is the right child of parent_i.
 *
 * Construct the binary tree described by `descriptions` and return _its **root**_.
 *
 * The test cases will be generated such that the binary tree is **valid**.
 *
 * **Example 1:**
 *
 * ![](https://assets.leetcode.com/uploads/2022/02/09/example1drawio.png)
 *
 * **Input:** descriptions = \[\[20,15,1],[20,17,0],[50,20,1],[50,80,0],[80,19,1]]
 *
 * **Output:** [50,20,80,15,17,19]
 *
 * **Explanation:** The root node is the node with value 50 since it has no parent.
 *
 * The resulting binary tree is shown in the diagram. 
 *
 * **Example 2:**
 *
 * ![](https://assets.leetcode.com/uploads/2022/02/09/example2drawio.png)
 *
 * **Input:** descriptions = \[\[1,2,1],[2,3,0],[3,4,1]]
 *
 * **Output:** [1,2,null,null,3,4]
 *
 * **Explanation:** The root node is the node with value 1 since it has no parent.
 *
 * The resulting binary tree is shown in the diagram. 
 *
 * **Constraints:**
 *
 * *   1 <= descriptions.length <= 10⁴
 * *   `descriptions[i].length == 3`
 * *   1 <= parent_i, child_i <= 10⁵
 * *   0 <= isLeft_i <= 1
 * *   The binary tree described by `descriptions` is valid.
**/
public class Solution {
    public TreeNode createBinaryTree(int[][] descriptions) {
        Map map = new HashMap<>();
        for (int[] description : descriptions) {
            Data data = map.get(description[0]);
            if (data == null) {
                data = new Data();
                data.node = new TreeNode(description[0]);
                data.isHead = true;
                map.put(description[0], data);
            }
            Data childData = map.get(description[1]);
            if (childData == null) {
                childData = new Data();
                childData.node = new TreeNode(description[1]);
                map.put(childData.node.val, childData);
            }
            childData.isHead = false;
            if (description[2] == 1) {
                data.node.left = childData.node;
            } else {
                data.node.right = childData.node;
            }
        }
        for (Map.Entry entry : map.entrySet()) {
            if (entry.getValue().isHead) {
                return entry.getValue().node;
            }
        }
        return null;
    }

    private static class Data {
        TreeNode node;
        boolean isHead;
    }
}