Number of Flowers in Full Bloom LeetCode solution in Java

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class Solution {
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  public int[] fullBloomFlowers(int[][] flowers, int[] persons) {
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    int n = persons.length;
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    int[] result = new int[n];
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    TreeMap<Integer, Integer> treeMap = new TreeMap<>();
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    // See explanation here:
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    // https://leetcode.com/problems/my-calendar-iii/discuss/109556/JavaC%2B%2B-Clean-Code
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    for (int[] flower : flowers) {
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      treeMap.put(flower[0], treeMap.getOrDefault(flower[0], 0) + 1);
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      // use end + 1 instead of end
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      treeMap.put(flower[1] + 1, treeMap.getOrDefault(flower[1] + 1, 0) - 1);
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    }
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    TreeMap<Integer, Integer> sum = new TreeMap<>();
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    int prev = 0;
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    for (Map.Entry<Integer, Integer> entry : treeMap.entrySet()) {
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      prev += entry.getValue();
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      sum.put(entry.getKey(), prev);
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    }
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    for (int i = 0; i < n; i++) {
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      Map.Entry<Integer, Integer> entry = sum.floorEntry(persons[i]);
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      // if entry is null then result[i] = 0
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      if (entry != null) result[i] = entry.getValue();
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    }
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    return result;
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  }
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}