1653. Minimum Deletions to Make String Balanced

Description

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 sbalanced.

 

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'​​.

 

Solutions

Solution: Dynamic Programming

• Time complexity: O(n)
• Space complexity: O(1)

 

JavaScript

/**
 * @param {string} s
 * @return {number}
 */
const minimumDeletions = function (s) {
  let a = (b = 0);

  for (const char of s) {
    char === 'a' ? (a = Math.min(b, a + 1)) : (b += 1);
  }
  return Math.min(a, b);
};