687. Longest Univalue Path

 /**
  * 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 ;
 }();

 class Solution
 {
 public:
     int res=;
     int longestUnivaluePath(TreeNode* root)
     {
         if(root==NULL)
             return ;
         count(root);
         return res;
     }

     int count(TreeNode* root)
     {
         int l=root->left?count(root->left):;
         int r=root->right?count(root->right):;
         int resl=root->left&&root->left->val==root->val?l+:;
         int resr=root->right&&root->right->val==root->val?r+:;
         res=max(res,resl+resr);
         return max(resl,resr);
     }
 };

这个题要注意一下，容易错，辅助遍历函数有返回值。