Longest ZigZag Path in a Binary Tree LeetCode solution in C++

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class Solution {
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 public:
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  int maxLength = 0;
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  void solve(TreeNode *root, int dir, int currLength) {
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    if (!root) return;
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    maxLength = max(maxLength, currLength);
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    solve(root->left, 0, dir ? currLength + 1 : 1);
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    solve(root->right, 1, dir ? 1 : currLength + 1);
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  }
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  int longestZigZag(TreeNode *root) {
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    solve(root, 0, 0);
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    solve(root, 1, 0);
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    return maxLength;
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  }
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};