Sandbox::https://github.com/prashanthigupta/leetcode-algorithms/blob/master/src/PositionsOfLargeGroups.java

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import java.util.ArrayList;

import java.util.List;

public class PositionsOfLargeGroups {

public List<List<Integer>> largeGroupPositions(String s) {

List<List<Integer>> result = new ArrayList<>();

char current = s.charAt(0);

int start = 0;

for (int index = 1 ; index < s.length() ; index++) {

if (s.charAt(index) != current) {

if (index - start >= 3) result.add(List.of(start, index - 1));

start = index;

current = s.charAt(index);

}

if (s.length() - start >= 3) result.add(List.of(start, s.length() - 1));

return result;

}