Formatted question description: https://leetcode.ca/all/830.html

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".

Call a group large if it has 3 or more characters.  We would like the starting and ending positions of every large group.

The final answer should be in lexicographic order.

 

Example 1:

Input: "abbxxxxzzy"
Output: [[3,6]]
Explanation: "xxxx" is the single large group with starting  3 and ending positions 6.

Example 2:

Input: "abc"
Output: []
Explanation: We have "a","b" and "c" but no large group.

Example 3:

Input: "abcdddeeeeaabbbcd"
Output: [[3,5],[6,9],[12,14]]

 

Note:  1 <= S.length <= 1000

Companies:
Adobe

Related Topics:
Array

Solution 1.

// OJ: https://leetcode.com/problems/positions-of-large-groups/

// Time: O(N)
// Space: O(1)
class Solution {
public:
    vector<vector<int>> largeGroupPositions(string S) {
        vector<vector<int>> ans;
        for (int N = S.size(), i = 0; i < N;) {
            int j = i + 1;
            while (j < N && S[j] == S[i]) ++j;
            if (j - i >= 3) ans.push_back({ i, j - 1 });
            i = j;
        }
        return ans;
    }
};

Java

class Solution {
    public List<List<Integer>> largeGroupPositions(String S) {
        List<List<Integer>> largeGroupPositions = new ArrayList<List<Integer>>();
        if (S.length() < 3)
            return largeGroupPositions;
        int begin = 0;
        char prev = S.charAt(0);
        int length = S.length();
        for (int i = 1; i < length; i++) {
            char c = S.charAt(i);
            if (c != prev) {
                if (i - begin >= 3) {
                    int end = i - 1;
                    List<Integer> largeGroupPosition = new ArrayList<Integer>();
                    largeGroupPosition.add(begin);
                    largeGroupPosition.add(end);
                    largeGroupPositions.add(largeGroupPosition);
                }
                begin = i;
            }
            prev = c;
        }
        if (length - begin >= 3) {
            int end = length - 1;
            List<Integer> largeGroupPosition = new ArrayList<Integer>();
            largeGroupPosition.add(begin);
            largeGroupPosition.add(end);
            largeGroupPositions.add(largeGroupPosition);
        }
        return largeGroupPositions;
    }
}

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