687. Longest Univalue Path

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687. Longest Univalue Path

Description

Given the root of a binary tree, return the length of the longest path, where each node in the path has the same value. This path may or may not pass through the root.

The length of the path between two nodes is represented by the number of edges between them.

Example 1:

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Input: root = [5,4,5,1,1,null,5]
Output: 2
Explanation: The shown image shows that the longest path of the same value (i.e. 5).

Example 2:

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Input: root = [1,4,5,4,4,null,5]
Output: 2
Explanation: The shown image shows that the longest path of the same value (i.e. 4).

Constraints:

  • The number of nodes in the tree is in the range [0, 10^4].
  • -1000 <= Node.val <= 1000
  • The depth of the tree will not exceed 1000.

Hints/Notes

  • binary 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 longestUnivaluePath(TreeNode* root) {
        if (!root) {
            return 0;
        }
        traverse(root, root->val);
        return res;
    }

    int traverse(TreeNode* root, int val) {
        if (!root) {
            return 0;
        }
        int left = traverse(root->left, root->val);
        int right = traverse(root->right, root->val);

        res = max(res, left + right);

        if (root->val != val) {
            return 0;
        }

        return max(left, right) + 1;
    }
};