java solution:BFS 算法
class Solution {
public int minMutation(String startGene, String endGene, String[] bank) {
//首先创建一个集合来存储有效基因串
Set<String> bankSet = new HashSet<>(Arrays.asList(bank));
if(!bankSet.contains(endGene)) return -1;
//初始化BFS所需的
char[] genes = new char[]{
'A', 'G', 'T', 'C'};
Queue<String> queue = new LinkedList<>();
queue.offer(startGene);
Set<String> visited = new HashSet<>();
visited.add(startGene);
int steps = 0;
while(