最小基因变化

/*
  思路：
  1. 由于Java Stream不适合直接处理BFS搜索，我们主要使用Stream来初始化数据结构。
  2. 使用Stream初始化基因库，并过滤出有效的序列。
*/
import java.util.*;
import java.util.stream.Collectors;
 
public class GeneMutationStream {
    public int minMutation(String start, String end, String[] bank) {
        Set<String> bankSet = Arrays.stream(bank).collect(Collectors.toSet());
        if (!bankSet.contains(end)) return -1;
 
        char[] genes = new char[]{'A', 'C', 'G', 'T'};
        Queue<String> queue = new LinkedList<>();
        queue.offer(start);
        Set<String> visited = new HashSet<>();
        visited.add(start);
        int level = 0;
 
        while (!queue.isEmpty()) {
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                String current = queue.poll();
                if (current.equals(end)) return level;
 
                char[] currentArray = current.toCharArray();
                for (int j = 0; j < currentArray.length; j++) {
                    char old = currentArray[j];
                    for (char c : genes) {
                        currentArray[j] = c;
                        String next = new String(currentArray);
                        if (bankSet.contains(next) && !visited.contains(next)) {
                            visited.add(next);
                            queue.offer(next);
                        }
                    }
                    currentArray[j] = old;
                }
            }
            level++;
        }
 
        return -1;
    }
}