// Author: Huahua
class Solution {
public:
  TreeNode *buildTree(vector<int> &inorder, vector<int> &postorder) {
    unordered_map<int, int> pos;
 
    for (int i = 0; i < inorder.size(); i++)
      pos[inorder[i]] = i;
 
    function<TreeNode*(int, int, int, int)> buildTree = [&](int is, int ie, int ps, int pe) {
      if (ps > pe) return (TreeNode*)nullptr;
 
      int im = pos[postorder[pe]];
      int pm = ps + (im - is) - 1;
 
      auto root = new TreeNode(postorder[pe]);
      root->left = buildTree(is, im - 1, ps, pm);
      root->right = buildTree(im + 1, ie, pm + 1, pe - 1);
      return root;
    };
 
    return buildTree(0, inorder.size() - 1, 0, postorder.size() - 1);
  }
};