Leetcode•Sep 05, 2025
Positions of Large Groups
Hazrat Ali
Leetcode
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".
Solution
/**
* @param {string} S
* @return {number[][]}
*/
const largeGroupPositions = S => {
const result = [];
let i = 0;
let j = 0;
while (j < S.length) {
while (j < S.length && S[i] === S[j]) {
j++;
}
const len = j - i;
if (len >= 3) {
result.push([i, j - 1]);
}
i = j;
}
return result;
};