Minimum Number of Taps to Open to Water a Garden LeetCode solution in Java

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class Solution {
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  public int minTaps(int n, int[] ranges) {
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    Integer[] idx = IntStream.range(0, ranges.length).boxed().toArray(Integer[]::new);
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    Arrays.sort(idx, Comparator.comparingInt(o -> o - ranges[o]));
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    int ans = 1, cur = 0, end = 0;
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    for (int i = 0; i < ranges.length && end < n; i++) {
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      int j = idx[i];
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      if (j - ranges[j] > cur) {
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        cur = end;
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        ans++;
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      }
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      if (j - ranges[j] <= cur) {
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        end = Math.max(end, j + ranges[j]);
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      }
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    }
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    return end < n ? -1 : ans;
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  }
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}