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".

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/
// Author: github.com/lzl124631x
// 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;
    }
};