lc298-Binary Tree Longest Consecutive Sequence

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/**
 * 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 {
private:
    int max_l = INT_MIN;
public:
    void sol(TreeNode* r, int prev, int cur_l) {
        if (r == nullptr) {
            if (cur_l > max_l) max_l = cur_l;
            cur_l = 1;
            return;
        }
        // cout << "val "<<r->val << " prev" << prev << " cur "<< cur_l << endl;
        if ((r -> val) == prev + 1)
            cur_l++;
        else {
            if (cur_l > max_l) max_l = cur_l;
            cur_l = 1;
        }
        sol(r->left, r->val, cur_l);
        sol(r->right, r->val, cur_l);
    }
    int longestConsecutive(TreeNode* root) {
        if (root == nullptr) return 0;
        sol(root, INT_MIN, 1);
        return max_l;
    }
};