【面試經】——全排列

先丟代碼,後續補充說明：

public class MainTest {

    private static int num = 0;

    public static void main(String[] args) {
        int[] ints = new int[]{1,2,3};
        int[] result = new int[ints.length];
        System.out.println("方案1：");
        pl2(ints,result,0);
        num=0;
        System.out.println("\n方案2：");
        pl(ints,0);
    }

    public static void pl2(int[] ints,int[] result,int start){
        int[] data = result.clone();
        if (ints.length == start){
            num++;
            System.out.println(num + " : " + Arrays.toString(result));
        }else {
            for (int i = 0 ;i < ints.length; i ++ ){
                boolean flag = true;
                for (int dd :data){
                    if (ints[i] == dd){
                        flag =false;
                        break;
                    }
                }

                Arrays.asList(result).contains(ints[i]); //爲何不能這麼判斷

                if (flag){
                    data[start] = ints[i];
                    pl2(ints,data,start+1);
                }
            }
        }
    }

    public static void pl (int[] ints , int start){
        if (ints.length == start){
            num++;
            System.out.println(num + " : "+ Arrays.toString(ints));
        }else {
            for (int i = start ; i < ints.length;i++){
                swap(ints,i,start);
                pl(ints,start+1);
                swap(ints,start,i);
            }
        }
    }

    private static void swap(int[] ints, int i, int start) {
        int mid = ints[i];
        ints[i] = ints[start];
        ints[start] = mid;
    }


}

• 有關ArrayList.asList().contains()參見【Java踩坑記】——Arrays.asList().contains()