import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class FindFirstNonRepeatCharacter {
    private static final int THREAD_POOL_SIZE = 4; // 线程池大小
    private static final int CHUNK_SIZE = 1000000; // 每个线程处理的字符数

    public static void main(String[] args) throws Exception {
        String input = "大约有3.7亿个字的字符串"; // 待处理的字符串

        ExecutorService executorService = Executors.newFixedThreadPool(THREAD_POOL_SIZE);
        Map<Character, Integer> characterCountMap = new HashMap<>();

        int start = 0;
        int end = CHUNK_SIZE;

        // 分割字符串，将每个子串交给一个线程处理
        while (start < input.length()) {
            if (end > input.length()) {
                end = input.length();
            }

            String chunk = input.substring(start, end);
            Callable<Map<Character, Integer>> callable = new CharacterCountTask(chunk);

            Future<Map<Character, Integer>> future = executorService.submit(callable);

            // 合并每个线程的结果到总的字符计数器中
            Map<Character, Integer> chunkCharacterCountMap = future.get();
            for (Map.Entry<Character, Integer> entry : chunkCharacterCountMap.entrySet()) {
                char character = entry.getKey();
                int count = entry.getValue();
                characterCountMap.put(character, characterCountMap.getOrDefault(character, 0) + count);
            }

            start = end;
            end += CHUNK_SIZE;
        }

        // 找到第一个不重复的字符
        char firstNonRepeatCharacter = '\0';
        for (int i = 0; i < input.length(); i++) {
            char character = input.charAt(i);
            if (characterCountMap.get(character) == 1) {
                firstNonRepeatCharacter = character;
                break;
            }
        }

        executorService.shutdown();

        System.out.println("第一个不重复的字符是：" + firstNonRepeatCharacter);
    }

    static class CharacterCountTask implements Callable<Map<Character, Integer>> {
        private final String input;

        CharacterCountTask(String input) {
            this.input = input;
        }

        @Override
        public Map<Character, Integer> call() {
            Map<Character, Integer> characterCountMap = new HashMap<>();
            for (int i = 0; i < input.length(); i++) {
                char character = input.charAt(i);
                characterCountMap.put(character, characterCountMap.getOrDefault(character, 0) + 1);
            }
            return characterCountMap;
        }
    }
}