LeetCode 1758: Minimum Changes To Make Alternating Binary String Solution

Master LeetCode problem 1758 (Minimum Changes To Make Alternating Binary String), a easy challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

1758. Minimum Changes To Make Alternating Binary String

Easy

String

Problem Explanation

Explanation:

To make the string alternating, we need to ensure that no two adjacent characters are equal. We can iterate over the string and count the number of changes needed if we consider the string starting with '0' as the first character and the number of changes needed if we consider the string starting with '1' as the first character. The minimum of these two counts will be our answer.

Initialize two counters count0 and count1 to count the number of changes needed when considering the string starting with '0' and '1' respectively.
Iterate over the string and check if the current index is expected to be '0' or '1' based on the starting character.
Increment the respective counter if the character at the current index is not as expected.
Return the minimum of count0 and count1.

Time Complexity:

The time complexity of this solution is O(n), where n is the length of the input string.

Space Complexity:

The space complexity is O(1) since we are using only a constant amount of extra space.

Solution Code

class Solution {
    public int minOperations(String s) {
        int count0 = 0, count1 = 0;
        
        for (int i = 0; i < s.length(); i++) {
            if (i % 2 == 0) {
                if (s.charAt(i) != '0') count0++;
                if (s.charAt(i) != '1') count1++;
            } else {
                if (s.charAt(i) != '1') count0++;
                if (s.charAt(i) != '0') count1++;
            }
        }
        
        return Math.min(count0, count1);
    }
}

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