LeetCode：105_Construct Binary Tree from Preorder and Inorder Traversal | 根据前序和中序遍历构建二叉树 | Medium

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：

struct TreeNode {
    int            val;
    TreeNode    *left;
    TreeNode    *right;
    TreeNode(int x): val(x),left(NULL), right(NULL) {}
};

typedef vector<int>::iterator Iter;
TreeNode *buildTree(vector<int> &preorder, vector<int> &inorder) 
{
    return buildTreeRecur(preorder.begin(), preorder.end(), inorder.begin(), inorder.end());
}

TreeNode *buildTreeRecur(Iter pstart, Iter pend, Iter istart, Iter iend)
{
    if(pstart == pend || istart == iend)
        return NULL;
    int ival = *pstart;
    Iter ipos = find(istart, iend, ival);
    TreeNode *res = new TreeNode(ival);
    res->left = buildTreeRecur(pstart + 1, pstart+1+(ipos-istart), istart, ipos);
    res->right = buildTreeRecur(pstart+1+(ipos-istart), pend, ipos+1, iend);
    return res;
}