Maximum Level Sum of a Binary Tree LeetCode solution in Java

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class Solution {
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  Map<Integer, Integer> map = new HashMap<>();
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  public void go(TreeNode root, int level) {
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    if (root == null) return;
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    if (map.containsKey(level)) {
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      map.put(level, map.get(level) + root.val);
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    } else {
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      map.put(level, root.val);
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    }
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    go(root.left, level + 1);
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    go(root.right, level + 1);
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  }
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  public int maxLevelSum(TreeNode root) {
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    go(root, 0);
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    int max = Integer.MIN_VALUE, ind = -1;
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    for (var i : map.entrySet()) {
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      if (max < i.getValue()) {
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        max = i.getValue();
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        ind = i.getKey();
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      }
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    }
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    return ind + 1;
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  }
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}