/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* buildSubTree(vector<int>& preorder, int pleft, int pright, vector<int>& inorder, int ileft, int iright) {
        if (pleft >= preorder.size() || ileft >= inorder.size()) return nullptr;
        if (pright < 0 || iright < 0) return nullptr;
        if (pright < pleft || iright < ileft) return nullptr;
        if (pleft == pright) return new TreeNode(preorder[pleft]);
        TreeNode* ret = new TreeNode;
        ret->val = preorder[pleft];
        int len = pright - pleft;
        for (int i = 0; i <= len; i++) {
            if (preorder[pleft] == inorder[i+ileft]) {
                ret->left = buildSubTree(preorder, pleft+1, pleft+i, inorder, ileft, ileft+i-1);
                ret->right = buildSubTree(preorder, pleft+1+i, pright, inorder, ileft+i+1, iright);
            }
        }
        return ret;
    }
    TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
        return buildSubTree(preorder, 0, preorder.size()-1, inorder, 0, inorder.size()-1);
    }
};