1422. Maximum Score After Splitting a String

#Problem

Given a string s of zeros and ones, return the maximum score after splitting the string into two non-empty substrings (i.e. left substring and right substring).

The score after splitting a string is the number of zeros in the left substring plus the number of ones in the right substring.

https://leetcode.com/problems/maximum-score-after-splitting-a-string/

Example 1:

Input: s = "011101"
Output: 5
Explanation:
All possible ways of splitting s into two non-empty substrings are:
left = "0" and right = "11101", score = 1 + 4 = 5
left = "01" and right = "1101", score = 1 + 3 = 4
left = "011" and right = "101", score = 1 + 2 = 3
left = "0111" and right = "01", score = 1 + 1 = 2
left = "01110" and right = "1", score = 2 + 1 = 3

Example 2:

Input: s = "00111"
Output: 5
Explanation: When left = "00" and right = "111", we get the maximum score = 2 + 3 = 5

Example 3:

Input: s = "1111" Output: 3

Constraints:

• 2 <= s.length <= 500
• The string s consists of characters '0' and '1' only.

#Test Cases

class Solution:
    def maxScore(self, s: str) -> int:

import pytest

from solution import Solution


@pytest.mark.parametrize('s, expected', [
    ("011101", 5),
    ("00111", 5),
    ("1111", 3),

    ("00", 1),
])
@pytest.mark.parametrize('sol', [Solution()])
def test_solution(sol, s, expected):
    assert sol.maxScore(s) == expected

#Thoughts

设 s 中一个有 one 个 '1'。从左到右遍历字符串，记录 '0' 和 '1' 的个数，设分别为 zero1 和 one1。那么 zero1 + (one - one1) 就是此时的 score。取最大的即可。

#Code

class Solution:
    def maxScore(self, s: str) -> int:
        max2 = lambda a, b: a if a >= b else b
        counts = [0, 0]
        counts[int(s[0])] += 1
        best = counts[0] - counts[1]
        for i in range(1, len(s) - 1):
            counts[int(s[i])] += 1
            best = max2(best, counts[0] - counts[1])

        counts[int(s[-1])] += 1
        return counts[1] + best