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) {
        if(preorder.size() == 1) return new TreeNode(preorder[0]);
        int indp = 1, indi = 0;
        stack<TreeNode*> st;
        st.push(new TreeNode(preorder[0]));
        TreeNode *res = st.top(), *lastpop, *temp;
        for(; indp < inorder.size(); indp++){
            if(st.top()->val != inorder[indi]){
                st.top()->left = new TreeNode(preorder[indp]);
                st.push(st.top()->left);
            }
            else{
                while(!st.empty() && st.top()->val == inorder[indi]){
                    lastpop = st.top();
                    st.pop();
                    indi++;
                }
                st.push(new TreeNode(preorder[indp]));
                lastpop->right = st.top();
            }
        }
        return res;
    }
};