543. Diameter of Binary Tree

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
static int wing=[]()
{
    std::ios::sync_with_stdio(false);
    cin.tie(NULL);
    return 0;
}();

class Solution 
{
public:
    int maxdiadepth=0;
    int diameterOfBinaryTree(TreeNode* root) 
    {
        countheight(root);
        return maxdiadepth;
    }
    
    int countheight (TreeNode* root)
    {
        if(root==NULL)
            return 0;
        int leftdepth=countheight(root->left);
        int rightdepth=countheight(root->right);
        maxdiadepth=max(maxdiadepth,leftdepth+rightdepth);
        return 1+max(leftdepth,rightdepth);
    }
};

递归求出以每个节点为转折点的最大直径长，取这些最大值中的最大值即可。