4Sum II LeetCode solution in Java

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class Solution {
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  public int fourSumCount(int[] nums1, int[] nums2, int[] nums3, int[] nums4) {
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    Map<Integer, Integer> map = new HashMap<>();
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    for (int k : nums3) for (int l : nums4) map.put(k + l, map.getOrDefault(k + l, 0) + 1);
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    int count = 0;
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    for (int i : nums1) for (int j : nums2) count += map.getOrDefault(-(i + j), 0);
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    return count;
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  }
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}