Given a binary tree, you need to find the length of Longest Consecutive Path in Binary Tree. 

Especially, this path can be either increasing or decreasing. For example, [1,2,3,4] and [4,3,2,1] are both considered valid, but the path [1,2,4,3] is not valid. On the other hand, the path can be in the child-Parent-child order, where not necessarily be parent-child order.

Example 1:

Input:        1       / \      2   3Output: 2Explanation: The longest consecutive path is [1, 2] or [2, 1].

 

Example 2:

Input:        2       / \      1   3Output: 3Explanation: The longest consecutive path is [1, 2, 3] or [3, 2, 1].

 

 

/** * 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 longestConsecutive(TreeNode* root) {        int longestLen = 0;        dfs(root,NULL,longestLen);        return longestLen;    }private:    pair
     
       dfs(TreeNode *root,TreeNode*pre,int &longestLen)     {        if(!root) return {
   0,0};        pair
      
        res1,res2;        pair
       
         left = dfs(root->left,root,longestLen);        pair
        
          right = dfs(root->right,root,longestLen);        longestLen = max(longestLen,left.first+right.second+1);        longestLen = max(longestLen,left.second+right.first+1);        int inc = 0, dec = 0;        if ( pre && root->val == pre->val + 1 ) {         inc = max(left.first, right.first) + 1;        }        if (pre&& root->val == pre->val - 1 ) {        dec = max(left.second, right.second) + 1;        }       return {inc,dec};     }};