Longest ZigZag Path in a Binary Tree 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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  static class Pair {
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    int left = -1;
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    int right = -1;
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    int maxLen = 0;
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  }
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  public int longestZigZag(TreeNode root) {
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    Pair ans = longestZigZag_(root);
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    return ans.maxLen;
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  }
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  public Pair longestZigZag_(TreeNode root) {
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    if (root == null) return new Pair();
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    Pair l = longestZigZag_(root.left);
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    Pair r = longestZigZag_(root.right);
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    Pair myAns = new Pair();
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    myAns.left = l.right + 1;
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    myAns.right = r.left + 1;
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    int max = Math.max(myAns.left, myAns.right);
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    myAns.maxLen = Math.max(max, Math.max(l.maxLen, r.maxLen));
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    return myAns;
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  }
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}