Most Frequent Subtree Sum LeetCode solution in Java

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class Solution {
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  public int[] findFrequentTreeSum(TreeNode root) {
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    HashMap<Integer, Integer> map = new HashMap<>();
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    int sum = sum(root, map);
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    int max = 0;
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    int count = 0;
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    for (Integer key : map.keySet()) {
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      max = Math.max(max, map.get(key));
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    }
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    for (Integer key : map.keySet()) {
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      if (max == map.get(key)) {
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        count++;
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      }
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    }
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    int[] ans = new int[count];
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    int counter = 0;
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    for (Integer key : map.keySet()) {
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      if (max == map.get(key)) {
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        ans[counter++] = key;
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      }
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    }
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    return ans;
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  }
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  public int sum(TreeNode root, HashMap<Integer, Integer> map) {
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    if (root == null) return 0;
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    int lh = sum(root.left, map);
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    int rh = sum(root.right, map);
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    map.put(lh + rh + root.val, map.getOrDefault(lh + rh + root.val, 0) + 1);
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    return lh + rh + root.val;
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  }
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}