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.

830. Positions of Large Groups
``````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);
}
``````