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".

A group is identified by an interval [start, end], where start and end denote the start and end indices (inclusive) of the group. In the above example, "xxxx" has the interval [3,6].

A group is considered large if it has 3 or more characters.

Return the intervals of every large group sorted in increasing order by start index.

 

Example 1:

Input: s = "abbxxxxzzy"
Output: [[3,6]]
Explanation: "xxxx" is the only large group with start index 3 and end index 6.

Example 2:

Input: s = "abc"
Output: []
Explanation: We have groups "a", "b", and "c", none of which are large groups.

Example 3:

Input: s = "abcdddeeeeaabbbcd"
Output: [[3,5],[6,9],[12,14]]
Explanation: The large groups are "ddd", "eeee", and "bbb".

Example 4:

Input: s = "aba"
Output: []

 

Constraints:

  • 1 <= s.length <= 1000
  • s contains lower-case English letters only.

Rust Solution

struct Solution;

struct Group {
    c: char,
    start: usize,
    end: usize,
}

impl Solution {
    fn large_group_positions(s: String) -> Vec<Vec<i32>> {
        let mut prev: Option<Group> = None;
        let mut groups: Vec<Group> = vec![];
        for (i, c) in s.chars().enumerate() {
            if let Some(prev_group) = prev {
                if prev_group.c == c {
                    prev = Some(Group {
                        c,
                        start: prev_group.start,
                        end: i,
                    });
                } else {
                    groups.push(prev_group);
                    prev = Some(Group {
                        c,
                        start: i,
                        end: i,
                    });
                }
            } else {
                prev = Some(Group {
                    c,
                    start: i,
                    end: i,
                });
            }
        }
        if let Some(prev_group) = prev {
            groups.push(prev_group);
        }

        groups
            .iter()
            .filter_map(|g| {
                let start = g.start;
                let end = g.end;
                if end - start > 1 {
                    Some(vec![start as i32, end as i32])
                } else {
                    None
                }
            })
            .collect()
    }
}

#[test]
fn test() {
    let s = "abbxxxxzzy".to_string();
    let res: Vec<Vec<i32>> = vec_vec_i32![[3, 6]];
    assert_eq!(Solution::large_group_positions(s), res);
    let s = "abc".to_string();
    let res: Vec<Vec<i32>> = vec![];
    assert_eq!(Solution::large_group_positions(s), res);
    let s = "abcdddeeeeaabbbcd".to_string();
    let res: Vec<Vec<i32>> = vec_vec_i32![[3, 5], [6, 9], [12, 14]];
    assert_eq!(Solution::large_group_positions(s), res);
}

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