c++ - 我正在尝试使用此代码查找二叉树的高度，但它始终返回0，有人可以告诉我为什么吗？

Question

我正在尝试使用此代码查找二叉树的高度，但它始终返回0，有人可以告诉我为什么吗？

int heightHelper(Node* root, int maxheight, int rootheight)
{

    if (root->right == nullptr && root->left == nullptr) { //checks if the node has a child
        if (maxheight < rootheight) {
            maxheight = rootheight;
        }
    }
    else { //if it has then increase height by 1
        rootheight += 1;

        if (root->left != nullptr) {
            heightHelper(root->left, maxheight, rootheight);
        }
        if (root->right != nullptr) {
            heightHelper(root->right, maxheight, rootheight);
        }
    }

    return maxheight; //return height
}

int height(Node* root)
{
    // Write your code here.

    return heightHelper(root, 0, 0); //root node base case
}

Answer 1

您正在混淆两种处理方式。使用指针或地址(int*和&maxheight)传递结果参数。在这种情况下，没有返回值。但是，这是一种编码风格，我主要只在硬件编程中才能看到。

否则，您可以返回结果。您已经有一个返回参数，只需修正该值的实际用法即可，因为您的代码将忽略它。

这是两种方法:

使用返回参数:

int heightHelper(Node* root, int height)
{

    if (root->right == nullptr && root->left == nullptr) { //checks if the node has a child
        return height;
    }
    else { //if it has then increase height by 1
        height += 1;
        int maxheight1;
        int maxheight2;

        if (root->left != nullptr) {
            maxheight1 = heightHelper(root->left, height);
        }
        if (root->right != nullptr) {
            maxheight2 = heightHelper(root->right, height);
        }

        // return maximum of the two
        if (maxheight1 > maxheight2) return maxheight1;
        else return maxheight2;
    }
}

int height(Node* root)
{
    // Write your code here.

    return heightHelper(root, height); //root node base case
}

使用指针参数。请注意，rootheight对于每个分支都是局部的，因此请勿将其作为指针传递。

void heightHelper(Node* root, int* maxheight_ptr, int rootheight)
    {

    if (root->right == nullptr && root->left == nullptr) { //checks if the node has a child
        if (*maxheight < rootheight) {
            *maxheight = rootheight;
        }
    }
    else { //if it has then increase height by 1
        rootheight += 1;

        if (root->left != nullptr) {
            heightHelper(root->left, maxheight_ptr, rootheight);
        }
        if (root->right != nullptr) {
            heightHelper(root->right, maxheight_ptr, rootheight);
        }
    }
}

int height(Node* root)
{
    // Write your code here.

    int maxheight = 0;


    heightHelper(root, &maxheight, 0); //pass the addresses of variables

    return maxheight;
}