Corporate Flight Bookings LeetCode solution in Java

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class Solution {
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  public int[] corpFlightBookings(int[][] bookings, int n) {
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    // nums all equals to zero
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    int[] nums = new int[n];
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    // construct the diffs
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    Difference df = new Difference(nums);
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    for (int[] booking : bookings) {
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      // pay attention to the index
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      int i = booking[0] - 1;
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      int j = booking[1] - 1;
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      int val = booking[2];
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      // increase nums[i..j] by val
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      df.increment(i, j, val);
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    }
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    // return the final array
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    return df.result();
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  }
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  class Difference {
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    // diff array
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    private int[] diff;
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    public Difference(int[] nums) {
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      assert nums.length > 0;
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      diff = new int[nums.length];
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      // construct the diffs
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      diff[0] = nums[0];
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      for (int i = 1; i < nums.length; i++) {
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        diff[i] = nums[i] - nums[i - 1];
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      }
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    }
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    // increase nums[i..j] by val
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    public void increment(int i, int j, int val) {
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      diff[i] += val;
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      if (j + 1 < diff.length) {
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        diff[j + 1] -= val;
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      }
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    }
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    public int[] result() {
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      int[] res = new int[diff.length];
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      // contract the diff array based on the result
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      res[0] = diff[0];
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      for (int i = 1; i < diff.length; i++) {
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        res[i] = res[i - 1] + diff[i];
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      }
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      return res;
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    }
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  }
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}