距离即为节点间的边数。

code:

struct Node
{
    Node* left;
    Node* right;
    int nmaxleft;
    int nmaxright;
    int vhvalue;
};

int ans;//答案

int findmaxval(Node* root)
{
    if (root == NULL) return;
    if (root->left == NULL) return root->nmaxleft = 0;
    if (root->right == NULL) return root->nmaxright = 0;
    if (root->left != NULL) findmaxval(root->left);
    if (root->right != NULL) findmaxval(root->right);
    if (root->left != NULL)
    {
        int tmp = 0;
        if (root->left->nmaxleft > root->left->nmaxright)
            tmp = root->left->nmaxleft;
        else
            tmp = root->left->nmaxright;
        root->nmaxleft = tmp + 1;
    }
    if (root->right != NULL)
    {
        int tmp = 0;
        if (root->right->nmaxleft > root->right->nmaxright)
            tmp = root->right->nmaxleft;
        else
            tmp = root->right->nmaxright;
        root->nmaxright = tmp + 1;
    }

    ans = max(ans, root->nmaxleft + root->nmaxright);
}