Only different with preorder and postorder is that the root start from the beginning for preorder.

1 /** 2  * Definition for binary tree 3  * struct TreeNode { 4  *     int val; 5  *     TreeNode *left; 6  *     TreeNode *right; 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} 8  * }; 9  */10 class Solution {11 public:12     TreeNode *getTree(vector
     
       &iv, vector
      
        &pv, int ist, int ied, int pst, int ped) {13         if (ist > ied) return NULL;14         int current = -1, len = 0;15         for (int i = ist; i <= ied; i++) {16             if (pv[pst] == iv[i]) {17                 current = i;18                 break;19             }20         }21         len = current - ist;22         TreeNode *root = new TreeNode(pv[pst]);23         root->left = getTree(iv, pv, ist, current-1, pst+1, pst+len);24         root->right = getTree(iv, pv, current+1, ied, pst+len+1, ped);25     }26     27     TreeNode *buildTree(vector
       
         &preorder, vector
        
          &inorder) {28         if (inorder.size() == 0 || inorder.size() != preorder.size()) return NULL;29         return getTree(inorder, preorder, 0, inorder.size()-1, 0, preorder.size()-1);30     }31 };