# 830. Positions of Large Groups

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`

``````class Solution {
public:
vector<vector<int>> largeGroupPositions(string S) {
vector<vector<int>> res;
int n = S.size(), i = 0, j = 0;
while (j < n) {
while (j < n && S[j] == S[i]) ++j;
if (j - i >= 3) res.push_back({i, j - 1});
i = j;
}
return res;
}
};
``````

``````class Solution {
public:
vector<vector<int>> largeGroupPositions(string S) {
vector<vector<int>> res;
int n = S.size(), start = 0;
for (int i = 1; i <= n; ++i) {
if (i < n && S[i] == S[start]) continue;
if (i - start >= 3) res.push_back({start, i - 1});
start = i;
}
return res;
}
};
``````

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

https://leetcode.com/problems/positions-of-large-groups/discuss/128961/Java-Solution-Two-Pointers

https://leetcode.com/problems/positions-of-large-groups/discuss/128942/My-Easy-7-Lines-C%2B%2B-Solution

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