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'
.
SOLUTION:
class Solution:
def minimumDeletions(self, s: str) -> int:
n = len(s)
minDel = float('inf')
curr = 0
for i in range(n + 1):
minDel = min(minDel, i - 2 * curr)
if i < n and s[i] == 'a':
curr += 1
minDel += curr
return minDel
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