题解 | #字符串的全部子序列#

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param s string字符串
     * @return string字符串一维数组
     */
  // 181ms 73%
    int n;
    public String[] generatePermutation (String s) {
        this.n = s.length();
        List<String> list = new ArrayList<>();
        list.add("");
        bfs(0, s, list);
        Set<String> hash = new HashSet<>(list);
        return hash.toArray(new String[hash.size()]);
    }
    
    public void bfs(int start, String s, List<String> list){
        if(start == n)
            return ;
        List<String> tmpList = new ArrayList<>(list);
        for(String tmp : tmpList){
            tmp += s.charAt(start);
            list.add(tmp);
        }
        bfs(start+1, s, list);
    }
}