数组的全排列

 private static int permanent(int []a,int start,int end){
        if(start == end){
            sum++;
            return sum;
        }
        for(int i=start;i<=end;i++){
            swap(a,start,i);
            permanent(a,start+1,end);
            swap(a,start,i);
        }
        return sum;
    }
    private static void swap(int []a,int x,int y){
        int temp = a[x];
        a[x] = a[y];
        a[y] = temp;
    }