为简单起见，假定数组长度相同，并且是
int数组。
int[] merge(int[] a, int[] b){ assert (a.length == b.length); int[] result = new int[a.length + b.length]; for (int i=0; i<a.length; i++) { result[i*2] = a[i]; result[i*2+1] = b[i]; } return result;}
