Longest Univalue Path LeetCode solution in Java

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/**
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 * Definition for a binary tree node. public class TreeNode { int val; TreeNode left; TreeNode
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 * right; TreeNode() {} TreeNode(int val) { this.val = val; } TreeNode(int val, TreeNode left,
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 * TreeNode right) { this.val = val; this.left = left; this.right = right; } }
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 */
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class Solution {
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  int maxLen = 0;
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  public int longestUnivaluePath(TreeNode root) {
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    lup(root);
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    return maxLen;
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  }
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  public int lup(TreeNode root) {
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    if (root == null) {
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      return 0;
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    }
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    int left = lup(root.left);
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    int right = lup(root.right);
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    int leftMax = 0;
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    int rightMax = 0;
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    if (root.left != null && root.val == root.left.val) {
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      leftMax = left + 1;
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    }
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    if (root.right != null && root.val == root.right.val) {
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      rightMax = right + 1;
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    }
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    maxLen = Math.max(maxLen, leftMax + rightMax);
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    return Math.max(leftMax, rightMax);
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  }
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}