Construct Binary Tree from Preorder and Inorder Traversal

<-M 105> Construct Binary Tree from Preorder and Inorder Traversal

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
        map<int,int> mp;
        for(int i = 0; i < inorder.size(); i++) {
            mp[inorder[i]] = i;
        }

        TreeNode* root = Tree(preorder, 0, preorder.size() - 1, inorder, 0, inorder.size() - 1, mp);
        return root;
    }

    TreeNode* Tree(vector<int>&preorder, int preStart, int preEnd, vector<int>&inorder, int inStart, int inEnd, map<int,int>&mp) {
         if (preStart > preEnd || inStart > inEnd)
             return NULL;

          TreeNode * root = new TreeNode(preorder[preStart]);
          int elem = mp[root->val];
          int nElem = elem - inStart;

          root->left = Tree(preorder, preStart + 1, preStart + nElem, inorder,
          inStart, elem - 1, mp);
          root->right = Tree(preorder, preStart + nElem + 1, preEnd, inorder,
          elem + 1, inEnd, mp);

          return root;
    }
};