2196 - Create Binary Tree From Descriptions

 JAVA

class Solution {
    public TreeNode createBinaryTree(int[][] descriptions) {
        Map<Integer, TreeNode> m = new HashMap<>();
        Set<Integer> vis = new HashSet<>();
        for (int[] d : descriptions) {
            int p = d[0], c = d[1], isLeft = d[2];
            if (!m.containsKey(p)) {
                m.put(p, new TreeNode(p));
            }
            if (!m.containsKey(c)) {
                m.put(c, new TreeNode(c));
            }
            if (isLeft == 1) {
                m.get(p).left = m.get(c);
            } else {
                m.get(p).right = m.get(c);
            }
            vis.add(c);
        }
        for (Map.Entry<Integer, TreeNode> entry : m.entrySet()) {
            if (!vis.contains(entry.getKey())) {
                return entry.getValue();
            }
        }
        return null;
    }
}

C++

class Solution {
public:
    TreeNode* createBinaryTree(vector<vector<int>>& A) {
        unordered_map<TreeNode*, TreeNode*> parentMap; // map from child node pointer to parent node pointer
        unordered_map<int, TreeNode*> m; // map from node value to node pointer
        for (auto &v : A) {
            int p = v[0], c = v[1], isLeft = v[2];
            auto parent = m.count(p) ? m[p] : (m[p] = new TreeNode(p));
            auto child = m.count(c) ? m[c] : (m[c] = new TreeNode(c));
            if (isLeft) parent->left = child;
            else parent->right = child;
            parentMap[child] = parent;
        }
        auto root = m.begin()->second; // Pick a random node pointer and keep traversing up until the node doesn't have any parents
        while (parentMap.count(root)) root = parentMap[root];
        return root;
    }
};