数组反转

 1 static void Reverse2(int[] a, int lo, int hi)
 2         {
 3             if (lo < hi)
 4             {
 5                 var t = a[lo];
 6                 a[lo] = a[hi];
 7                 a[hi] = t;
 8                 Reverse2(a, lo + 1, hi - 1);
 9             }
10         }