content: package by.andd3dfx.string;
  
  import java.util.ArrayList;
  import java.util.List;
  
  /**
   * <pre>
   * <a href="https://leetcode.com/problems/positions-of-large-groups/description/">Task description</a>
   *
   * In a string s of lowercase letters, these letters form consecutive groups of the same character.
   * For example, a string like s = "abbxxxxzyy" has the groups "a", "bb", "xxxx", "z", and "yy".
   * A group is identified by an interval [start, end], where start and end denote the start and end indices (inclusive)
   * of the group. In the above example, "xxxx" has the interval [3,6].
   * A group is considered large if it has 3 or more characters.
   * Return the intervals of every large group sorted in increasing order by start index.
   *
   * Example 1:
   *   Input: s = "abbxxxxzzy"
   *   Output: [[3,6]]
   *   Explanation: "xxxx" is the only large group with start index 3 and end index 6.
   *
   * Example 2:
   *   Input: s = "abc"
   *   Output: []
   *   Explanation: We have groups "a", "b", and "c", none of which are large groups.
   *
   * Example 3:
   *   Input: s = "abcdddeeeeaabbbcd"
   *   Output: [[3,5],[6,9],[12,14]]
   *   Explanation: The large groups are "ddd", "eeee", and "bbb".
   *
   * Constraints:
   *     1 <= s.length <= 1000
   *     s contains lowercase English letters only.
   * </pre>
   *
   * @see <a href="https://youtu.be/RFTK3bFpLcs">Video solution</a>
   */
  public class LargeGroupPositions {
  
      public List<List<Integer>> find(String s) {
          if (s == null || s.length() < 3) {
              return List.of();
          }
  
          var result = new ArrayList<List<Integer>>();
          var chars = s.toCharArray();
  
          var start = 0;
          var pos = 1;
          while (pos < chars.length) {
              if (chars[pos] != chars[pos - 1]) {
                  addNewIntervalIfPossible(result, start, pos);
                  start = pos;
              }
              pos++;
          }
          addNewIntervalIfPossible(result, start, pos);
  
          return result;
      }
  
      private void addNewIntervalIfPossible(List<List<Integer>> result, int start, int pos) {
          if (pos - start >= 3) {
              result.add(List.of(start, pos - 1));
          }
      }
  }
  