821. Shortest Distance to a Character

Given a string s and a character c that occurs in s, return an array of integers answer where answer.length == s.length and answer[i] is the distance from index i to the closest occurrence of character c in s.

The distance between two indices i and j is abs(i - j), where abs is the absolute value function.

 

Example 1:

Input: s = "loveleetcode", c = "e"
Output: [3,2,1,0,1,0,0,1,2,2,1,0]
Explanation: The character 'e' appears at indices 3, 5, 6, and 11 (0-indexed).
The closest occurrence of 'e' for index 0 is at index 3, so the distance is abs(0 - 3) = 3.
The closest occurrence of 'e' for index 1 is at index 3, so the distance is abs(1 - 3) = 3.
For index 4, there is a tie between the 'e' at index 3 and the 'e' at index 5, but the distance is still the same: abs(4 - 3) == abs(4 - 5) = 1.
The closest occurrence of 'e' for index 8 is at index 6, so the distance is abs(8 - 6) = 2.

Example 2:

Input: s = "aaab", c = "b"
Output: [3,2,1,0]

 

Constraints:

  • 1 <= s.length <= 104
  • s[i] and c are lowercase English letters.
  • It is guaranteed that c occurs at least once in s.

Rust Solution

struct Solution;

impl Solution {
    fn shortest_to_char(s: String, c: char) -> Vec<i32> {
        let s: Vec<char> = s.chars().collect();
        let mut prev: Option<usize> = None;
        let n = s.len();
        let mut res: Vec<i32> = vec![n as i32; n];
        for i in 0..n {
            if s[i] == c {
                prev = Some(i);
            }
            if let Some(j) = prev {
                res[i] = i32::min(res[i], (i - j) as i32);
            }
        }
        prev = None;
        for i in (0..n).rev() {
            if s[i] == c {
                prev = Some(i);
            }
            if let Some(j) = prev {
                res[i] = i32::min(res[i], (j - i) as i32);
            }
        }
        res
    }
}

#[test]
fn test() {
    let s = "loveleetcode".to_string();
    let t = vec![3, 2, 1, 0, 1, 0, 0, 1, 2, 2, 1, 0];
    assert_eq!(Solution::shortest_to_char(s, 'e'), t);
}

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