矢量切片与矢量切片的树生成从预订和顺序矢量

Question

I'm getting the following error:

solution.cpp: In member function buildTree Line 26: Char 62: error: no matching function for call to 'Solution::buildTree(__gnu_cxx::__alloc_traits, int>::value_type*, std::vector*)' root->left = buildTree(&preorder[index],&inorderslice); ^

In this code:

class Solution {
public:
    TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
        if(preorder.empty() || inorder.empty())
            return NULL;
        if(preorder.size() == 1) // preorder and inorder should always have the same length
        {
            TreeNode *node = new TreeNode(preorder[0]);
            return node;
        }
        // current root is the first entry of preorder
        TreeNode *root = new TreeNode(preorder[0]);
        // find the index of this number in inorder
        std::vector<int>::iterator it = std::find(inorder.begin(), inorder.end(), preorder[0]);
        int index = std::distance(inorder.begin(), it);
        std::vector<int> inorderslice = std::vector<int>(inorder.begin(), inorder.begin() + index);
        root->left = buildTree(&preorder[index],&inorderslice); // This line is a problem
        root->right = buildTree(&preorder[index+1],&inorder[index+1]); // This line is a problem
        return root;

    }
};

I'm trying to solve a problem to generate a tree from its preorder and inorder traverse vectors.

I'm trying to do it recursively but I'm having a problem matching the variable types of the function doing the recursion.

    TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {

This header is receiving a pointer to a vector of ints.

In my algorithm I'm trying to slice the input vectors to only use parts of it in my recursion:

        std::vector<int> inorderslice = std::vector<int>(inorder.begin(), inorder.begin() + index);

For the preorder vector I just want to cut the elements in front (the ones before index), so I thought I'd just pass a pointer to that element of the vector.

For the inorder vector I want to cut the elements AFTER index.

In a pythonic way this would just be preorder[index:] inorder[:index]

But I'm getting an error in the call to the function.

How do I do this in C++?

Thank you.

Answer 1

Your functions take references; you're passing pointers.

There is a confusion here about what & means.

It is any of:

• the bitwise AND operator when applied in between two expressions
• the "address-of" operator when applied to one operator, resulting in a pointer
  • this is what you're doing in your function calls
• "reference" when added to a type name
  • this is what you're putting in your function parameters

In short, remove & from your calls, and review the chapter in your C++ book about using references.

This header is receiving a pointer to a vector of ints.

No, it isn't.