549

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
    int maxLen = 0;
public:
    int longestConsecutive(TreeNode* root) {
        dfs(root);
        return maxLen;
    }

    vector<int> dfs(TreeNode *root){
        if(!root) return {0,0};
        vector<int> curr(2, 1);

        if(root->left){
            vector<int> left = dfs(root->left);
            if(root->val == root->left->val+1)
                curr[1] = left[1]+1;
            else if(root->val == root->left->val-1)
                curr[0] = left[0]+1;
        }
        if(root->right){
            vector<int> right = dfs(root->right);
            if(root->val == root->right->val+1){
                curr[1] = max(curr[1], right[1]+1);
            }
            else if(root->val == root->right->val-1){
                curr[0] = max(curr[0], right[0]+1);
            }
        }
        maxLen = max(maxLen, curr[0]+curr[1]-1);
        return curr;
    }

};