298. Binary Tree Longest Consecutive Sequence

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298. Binary Tree Longest Consecutive Sequence

Description

Given the root of a binary tree, return the length of the longest consecutive sequence path .

A consecutive sequence path is a path where the values increase by one along the path.

Note that the path can start at any node in the tree, and you cannot go from a node to its parent in the path.

Example 1:

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Input: root = [1,null,3,2,4,null,null,null,5]
Output: 3
Explanation: Longest consecutive sequence path is 3-4-5, so return 3.

Example 2:

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Input: root = [2,null,3,2,null,1]
Output: 2
Explanation: Longest consecutive sequence path is 2-3, not 3-2-1, so return 2.

Constraints:

  • The number of nodes in the tree is in the range [1, 3 * 10^4].
  • -3 * 10^4 <= Node.val <= 3 * 10^4

Hints/Notes

  • traverse the tree

Solution

Language: C++

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/**
 * 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 res = 0;

    int longestConsecutive(TreeNode* root) {
        traverse(root, 1);
        return res;
    }

    void traverse(TreeNode* root, int cur) {
        if (root->left) {
            if (root->left->val == root->val + 1) {
                traverse(root->left, cur + 1);
            } else {
                traverse(root->left, 1);
            }
        }
        if (root->right) {
            if (root->right->val == root->val + 1) {
                traverse(root->right, cur + 1);
            } else {
                traverse(root->right, 1);
            }
        }
        res = max(res, cur);
    }
};