LeetCode-in-All

56. Merge Intervals

Medium

Given an array of intervals where intervals[i] = [starti, endi], merge all overlapping intervals, and return an array of the non-overlapping intervals that cover all the intervals in the input.

Example 1:

Input: intervals = [[1,3],[2,6],[8,10],[15,18]]

Output: [[1,6],[8,10],[15,18]]

Explanation: Since intervals [1,3] and [2,6] overlap, merge them into [1,6].

Example 2:

Input: intervals = [[1,4],[4,5]]

Output: [[1,5]]

Explanation: Intervals [1,4] and [4,5] are considered overlapping.

Constraints:

• 1 <= intervals.length <= 104
• intervals[i].length == 2
• 0 <= starti <= endi <= 104

Solution

defmodule Solution do
  @spec merge(intervals :: [[integer]]) :: [[integer]]
  def merge(intervals) do
    intervals
    |> Enum.sort_by(&hd(&1))
    |> Enum.reduce([], fn [start, finish], acc ->
      case acc do
        [] -> [[start, finish]]
        [[prev_start, prev_finish] | rest] ->
          if prev_finish >= start do
            # Merge overlapping intervals
            [[prev_start, max(prev_finish, finish)] | rest]
          else
            # No overlap
            [[start, finish] | acc]
          end
      end
    end)
    |> Enum.reverse()
  end
end

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