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;
        }
    }
    
  • // 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;
        }
    };
    
  • class Solution:
        def largeGroupPositions(self, S):
            """
            :type S: str
            :rtype: List[List[int]]
            """
            groups = []
            before_index, before_char = 0, S[0]
            for i, s in enumerate(S):
                if s != before_char:
                    if i - before_index >= 3:
                        groups.append([before_index, i - 1])
                    before_index = i
                    before_char = s
            if i - before_index >= 2:
                groups.append([before_index, i])
            return groups
    

All Problems

All Solutions