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56. Merge Intervals 👍

  • Time: $O(\texttt{sort})$
  • Space: $O(n)$
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class Solution {
 public:
  vector<vector<int>> merge(vector<vector<int>>& intervals) {
    vector<vector<int>> ans;

    ranges::sort(intervals);

    for (const vector<int>& interval : intervals)
      if (ans.empty() || ans.back()[1] < interval[0])
        ans.push_back(interval);
      else
        ans.back()[1] = max(ans.back()[1], interval[1]);

    return ans;
  }
};

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class Solution {
  public int[][] merge(int[][] intervals) {
    List<int[]> ans = new ArrayList<>();

    Arrays.sort(intervals, (a, b) -> Integer.compare(a[0], b[0]));

    for (int[] interval : intervals)
      if (ans.isEmpty() || ans.get(ans.size() - 1)[1] < interval[0])
        ans.add(interval);
      else
        ans.get(ans.size() - 1)[1] = Math.max(ans.get(ans.size() - 1)[1], interval[1]);

    return ans.toArray(int[][] ::new);
  }
}

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class Solution:
  def merge(self, intervals: list[list[int]]) -> list[list[int]]:
    ans = []

    for interval in sorted(intervals):
      if not ans or ans[-1][1] < interval[0]:
        ans.append(interval)
      else:
        ans[-1][1] = max(ans[-1][1], interval[1])

    return ans

var merge = function(intervals) {
  intervals.sort((a, b) => a[0] - b[0]);
  const res = [intervals[0]];
  for (let i = 1; i < intervals.length; i++) {
    const last = res[res.length - 1];
    if (intervals[i][0] <= last[1]) last[1] = Math.max(last[1], intervals[i][1]);
    else res.push(intervals[i]);
  }
  return res;
};
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