LeetCode 543. 二叉树的直径

题目链接：https://leetcode-cn.com/problems/diameter-of-binary-tree/

给定一棵二叉树，你需要计算它的直径长度。一棵二叉树的直径长度是任意两个结点路径长度中的最大值。这条路径可能穿过根结点。

 思路：返回根节点左右子树的高度和

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int diameterOfBinaryTree(TreeNode* root)
    {
        int dist=0;
        dfs(root,dist);
        return dist;
    }
    int dfs(TreeNode *root, int &dist)
    {
        if(root==nullptr)return 0;
        int left=dfs(root->left,dist);
        int right=dfs(root->right,dist);
        dist=max(left+right,dist);
        return max(left,right) + 1;
    }
};