1864. Minimum Number of Swaps to Make the Binary String Alternating

Problem

Given a binary string s, return **the *minimum* number of character swaps to make it alternating, or -1 if it is impossible.**

The string is called alternating if no two adjacent characters are equal. For example, the strings "010" and "1010" are alternating, while the string "0100" is not.

Any two characters may be swapped, even if they are not adjacent.

  Example 1:

Input: s = "111000"
Output: 1
Explanation: Swap positions 1 and 4: "111000" -> "101010"
The string is now alternating.

Example 2:

Input: s = "010"
Output: 0
Explanation: The string is already alternating, no swaps are needed.

Example 3:

Input: s = "1110"
Output: -1

  Constraints:

• 1 <= s.length <= 1000

• s[i] is either '0' or '1'.

Solution (Java)

class Solution {
    public int minSwaps(String s) {
        int[][] count = new int[2][2];
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if (i % 2 == 0) {
                count[0][c - '0']++;
            } else {
                count[1][c - '0']++;
            }
        }
        if ((count[0][0] == 0 && count[1][1] == 0) || (count[0][1] == 0 && count[1][0] == 0)) {
            return 0;
        }
        if (count[0][0] != count[1][1] && count[0][1] != count[1][0]) {
            return -1;
        }
        int ans1 = count[0][0] == count[1][1] ? count[0][0] : Integer.MAX_VALUE;
        int ans2 = count[0][1] == count[1][0] ? count[0][1] : Integer.MAX_VALUE;
        return Math.min(ans1, ans2);
    }
}

Explain:

nope.

Complexity:

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