给一个字符串abcd 然后再两两组合 三三组合

[qq_25451779]

如： ab ac ad bc bd cb abc abd bcd bca

从左往右 和从右往左 都需要
求大神给段代码最好再详解，


明天面试

[普凡]

public static void main(String[] args) {
    
        String arr[] = { "a", "b", "c", "d" };
        int all = 4;
        for (int i = 0; i < 1 << all; i++) {
            StringBuffer sb = new StringBuffer();
            for (int j = 0; j < all; j++) {
                if ((i & (1 << j)) != 0) {
                    sb.append(arr[j]);
                }
            }
            System.out.println(sb);
        }
    }

[雨季余静]

   List<String> result = new ArrayList<>();
    @Test
    public void test() {
        String[] target = new String[]{"a", "b", "c", "d"};
        for (int i = 1; i <= target.length; i++)
            calc(i, "", target);
        System.out.println(Arrays.toString(result.toArray()));
    }

    //递归
    public void calc(int length, String p, String... target) {
        for (String item : target)
            if (!p.contains(item) && (!((length == 1) && result.add(p + item))))
                calc(length - 1, p + item, target);
    }

[ssson]

public class Abcd { private static final String[] str = { "a", "b", "c", "d" }; private static String res = ""; int len = str.length; public static void main(String[] args) { t2(); t3(); } private static void t2() { for (int i = 0; i < str.length; i++) { res = str[i]; for (int j = 0; j < str.length; j++) { System.out.println(res + str[j]); } } } private static void t3() { for (int i = 0; i < str.length; i++) { res = str[i]; for (int j = 0; j < str.length; j++) { // System.out.println(res + str[j]); for (int k = 0; k < str.length; k++) { System.out.println(res + str[j] + str[k]); } } } } }