字符串排列组合Java版

C++链接：字符串的排列组合问题_NEOMc的博客-CSDN博客

char[] t1 = new char[]{'a', 'b', 'c', 'd'};
//        char[] t1 = new char[]{'a', 'b', 'c'};

        permutation(t1, 0, 4);
        for(int i=1; i<= 4; ++i)
            combination(t1, 0, i, new ArrayList());

public static void permutation(char[] data, int begin, int end) {
        if(begin == end -1) {
            System.out.println(data);
            return ;
        }

        for(int i=begin; i res) {
        if(m == 0) {
            System.out.println(res);
            return;
        }

        if(begin == data.length) {
            return;
        }

        res.add(data[begin]);
        combination(data, begin+1, m-1, res);
        res.remove(res.size()-1);
        combination(data, begin+1, m, res);
    }