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Java-based LeetCode algorithm problem solutions, regularly updated

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package g0601_0700.s0687_longest_univalue_path;

// #Medium #Depth_First_Search #Tree #Binary_Tree

import com_github_leetcode.TreeNode;

public class Solution {
    public int longestUnivaluePath(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int[] res = new int[1];
        preorderLongestSinglePathLen(root, res);
        return res[0];
    }

    private int preorderLongestSinglePathLen(TreeNode root, int[] res) {
        if (root == null) {
            return -1;
        }
        int left = preorderLongestSinglePathLen(root.left, res);
        int right = preorderLongestSinglePathLen(root.right, res);

        if (root.left == null || root.val == root.left.val) {
            left = left + 1;
        } else {
            left = 0;
        }

        if (root.right == null || root.val == root.right.val) {
            right = right + 1;
        } else {
            right = 0;
        }
        int longestPathLenPassingThroughRoot = left + right;
        res[0] = Math.max(res[0], longestPathLenPassingThroughRoot);
        return Math.max(left, right);
    }
}