2196. Create Binary Tree From Descriptions

class Solution {
public:
    TreeNode* createBinaryTree(vector<vector<int>>& descriptions) {

        unordered_map<int, TreeNode*> mp;
        unordered_set<int> st;

        for(auto desc: descriptions){

            int p = desc[0];
            int c = desc[1];
            int left = desc[2];

            if(mp.find(p) == mp.end()){
                mp[p] = new TreeNode(p);
            }

            if(mp.find(c) == mp.end()){
                mp[c] = new TreeNode(c);
            }

            if(left == 1){
                mp[p]->left = mp[c];
            }else{
                mp[p]->right = mp[c];
            }

            st.insert(c);
            
        }

        for(auto desc: descriptions){

            int p = desc[0];

            if(st.find(p) == st.end()){
                return mp[p];
            }
            
        }

        return nullptr;
        
    }
};