1653. Minimum Deletions to Make String Balanced

You are given a string s consisting only of characters 'a' and 'b'​​​​.

You can delete any number of characters in s to make s balanced. s is balanced if there is no pair of indices (i,j) such that i < j and s[i] = 'b' and s[j]= 'a'.

Return the minimum number of deletions needed to make s balanced.

 

Example 1:

Input: s = "aababbab"
Output: 2
Explanation: You can either:
Delete the characters at 0-indexed positions 2 and 6 ("aababbab" -> "aaabbb"), or
Delete the characters at 0-indexed positions 3 and 6 ("aababbab" -> "aabbbb").

Example 2:

Input: s = "bbaaaaabb"
Output: 2
Explanation: The only solution is to delete the first two characters.

 

Constraints:

  • 1 <= s.length <= 105
  • s[i] is 'a' or 'b'​​.

Rust Solution

struct Solution;

impl Solution {
    fn minimum_deletions(s: String) -> i32 {
        let n = s.len();
        let mut a = 0;
        let mut b = 0;
        for c in s.chars() {
            if c == 'a' {
                a += 1;
            } else {
                b += 1;
                b = b.max(a + 1);
            }
        }
        (n - a.max(b)) as i32
    }
}

#[test]
fn test() {
    let s = "aababbab".to_string();
    let res = 2;
    assert_eq!(Solution::minimum_deletions(s), res);
    let s = "bbaaaaabb".to_string();
    let res = 2;
    assert_eq!(Solution::minimum_deletions(s), res);
}

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