solution.java

import java.util.PriorityQueue;

class Solution {
    public String longestDiverseString(int a, int b, int c) {
        // Priority queue to store the characters and their counts.
        PriorityQueue<int[]> pq = new PriorityQueue<>((x, y) -> y[0] - x[0]);
        if (a > 0)
            pq.offer(new int[] { a, 'a' });
        if (b > 0)
            pq.offer(new int[] { b, 'b' });
        if (c > 0)
            pq.offer(new int[] { c, 'c' });

        StringBuilder result = new StringBuilder();

        while (!pq.isEmpty()) {
            int[] first = pq.poll();

            // Check if last two characters are the same.
            if (result.length() >= 2 && result.charAt(result.length() - 1) == first[1] &&
                    result.charAt(result.length() - 2) == first[1]) {

                if (pq.isEmpty())
                    break; // No more valid characters.

                // Pick the second character.
                int[] second = pq.poll();
                result.append((char) second[1]);
                second[0]--;

                if (second[0] > 0)
                    pq.offer(second);
                pq.offer(first);
            } else {
                result.append((char) first[1]);
                first[0]--;

                if (first[0] > 0)
                    pq.offer(first);
            }
        }

        return result.toString();
    }
}