Minimum Changes To Make Alternating Binary String — LeetCode 1758 Python Solution

The problem

You are given a string s consisting only of the characters '0' and '1'. In one operation, you can change any '0' to '1' or vice versa.

Example

Input

s = "0100"

Output

1

Explanation

If you change the last character to '1', s will be "0101", which is alternating.

Python solution

class Solution:
    def minOperations(self, s: str) -> int:
        cnt = sum(c != '01'[i & 1] for i, c in enumerate(s))
        return min(cnt, len(s) - cnt)

Complexity

Pattern: Hash Map

Trade memory for time: remember what you have seen so the second pass never happens. LeetCode 1758. Minimum Changes To Make Alternating Binary String is filed here because the reference solution below belongs to the algorithm family this hub collects, even though its LeetCode tags point elsewhere.

The hash map guide has the Python template for the pattern and the 709 LeetCode problems that use it.

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