LeetCode [830] Positions of Large Groups

 830. Positions of Large Groups

Easy

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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class Solution { public List<List<Integer>> largeGroupPositions(String s) { List<List<Integer>> ret = new ArrayList<>(); int n = s.length(), i=0, j=0; while(j<n){ while(j<n && s.charAt(i)==s.charAt(j)){ j++; } if(j-i>=3){ ret.add(Arrays.asList(new Integer[] {i, j-1})); } i=j; } return ret; } }