要求：通过二叉树的前序和中序遍历序列构建一颗二叉树

代码如下：

1 struct TreeNode { 2     int            val; 3     TreeNode    *left; 4     TreeNode    *right; 5     TreeNode(int x): val(x),left(NULL), right(NULL) {} 6 }; 7  8 typedef vector
     
      ::iterator Iter; 9 TreeNode *buildTree(vector
      
        &preorder, vector
       
         &inorder) 10 {11     return buildTreeRecur(preorder.begin(), preorder.end(), inorder.begin(), inorder.end());12 }13 14 TreeNode *buildTreeRecur(Iter pstart, Iter pend, Iter istart, Iter iend)15 {16     if(pstart == pend || istart == iend)17         return NULL;18     int ival = *pstart;19     Iter ipos = find(istart, iend, ival);20     TreeNode *res = new TreeNode(ival);21     res->left = buildTreeRecur(pstart + 1, pstart+1+(ipos-istart), istart, ipos);22     res->right = buildTreeRecur(pstart+1+(ipos-istart), pend, ipos+1, iend);23     return res;24 }