construct-binary-search-tree-from-preorder-traversal.cpp

class Solution {
public:
    TreeNode* bstFromPreorder(vector<int>& preorder, int& index, int parentIndex) {
        if(index >= preorder.size() || (parentIndex >= 0 && preorder[index] >= preorder[parentIndex])){
            return nullptr;
        }
        else{
            TreeNode* root = new TreeNode(preorder[index]);
            int thisIndex = index;
            index++;
            root->left = bstFromPreorder(preorder, index, thisIndex);
            root->right = bstFromPreorder(preorder, index, parentIndex);
            return root;
        }
    }
    
    TreeNode* bstFromPreorder(vector<int>& preorder) {
        int index = 0;
        return bstFromPreorder(preorder, index, -1);
    }
};