Solution.cpp

/**
 * 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 {
public:
    int ans;

    int longestConsecutive(TreeNode* root) {
        ans = 0;
        dfs(root);
        return ans;
    }

    vector<int> dfs(TreeNode* root) {
        if (!root) return {0, 0};
        int incr = 1, decr = 1;
        auto left = dfs(root->left);
        auto right = dfs(root->right);
        if (root->left) {
            if (root->left->val + 1 == root->val) incr = left[0] + 1;
            if (root->left->val - 1 == root->val) decr = left[1] + 1;
        }
        if (root->right) {
            if (root->right->val + 1 == root->val) incr = max(incr, right[0] + 1);
            if (root->right->val - 1 == root->val) decr = max(decr, right[1] + 1);
        }
        ans = max(ans, incr + decr - 1);
        return {incr, decr};
    }
};