830. Positions of Large Groups.md

830. Positions of Large Groups

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leetcode-cn Daily Challenge on January 5th, 2021.

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Difficulty : Easy

Related Topics : Array

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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".

Example 4:

Input: s = "aba"
Output: []

Constraints:

• 1 <= s.length <= 1000
• s contains lower-case English letters only.

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Solution

• mine
  • Java
    • Runtime: 2 ms, faster than 37.20%, Memory Usage: 39.1 MB, less than 76.81% of Java online submissions

      public List<List<Integer>> largeGroupPositions(String s) {
          List<List<Integer>> res = new ArrayList<>();
          int t = 0;
          char[] arr = s.toCharArray();
          for(int i = 0; i < arr.length; i++){
              if(i == 0){
                  t++;
              }else{
                  if(arr[i] == arr[i - 1]){
                      t++;
                  }else{
                      if(t >= 3){
                          res.add(Arrays.asList(i - t, i - 1));
                      }
                      t = 1;
                  }
              }
              if(i + 1 == arr.length && t >= 3){
                  res.add(Arrays.asList(i + 1 - t, i));
              }
          }
          return res;
      }
      

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