105. Construct Binary Tree from Preorder and Inorder Traversal

已知前序序列和中序序列，构建二叉树。

解法：递归

    TreeNode *build(vector& preorder, int preStart, int preEnd, 
                    vector &inorder, int inStart, int inEnd)
    {
        if(preStart > preEnd || inStart > inEnd)
            return NULL;
        
        
        
        int i = inStart;
        for(; i <= inEnd; ++i)
        {
            if(preorder[preStart] == inorder[i])
                break;
        }
        
        TreeNode *p = new TreeNode(preorder[preStart]);
        int leftLen = i - inStart;
        
        p->left = build(preorder, preStart + 1,  preStart + leftLen, inorder, inStart, i-1);
        p->right = build(preorder, preStart + 1 + leftLen, preEnd, inorder, i+1, inEnd);
        return p;
    }
    
    TreeNode* buildTree(vector& preorder, vector& inorder) {
        return build(preorder, 0, preorder.size()-1, inorder, 0, inorder.size()-1);
    }