很有趣的一道题，。

1 #include 
      
        2 #include 
       
         3 #include 
        
          4 #include 
         
           5 using namespace std; 6  7 const int maxn = 200000 + 10; 8 const int maxm = 1000000 + 10; 9 10 int a[maxn], f[maxm];11 12 int main()13 {14     int n; scanf("%d", &n);15     for(int i = 0; i < n; i++) scanf("%d", a + i);16     sort(a, a + n);17     n = unique(a, a + n) - a;18 19     int M = a[n-1];20     for(int i = 0; i < n; i++)21         for(int j = a[i] + 1; j <= a[i+1]; j++) f[j] = a[i];22 23     int ans = 0;24     for(int i = 0; i < n; i++)25     {26         for(int j = a[i] * 2; j <= M; j += a[i])27         {28             ans = max(ans, f[j] % a[i]);29         }30         ans = max(ans, M % a[i]);31     }32     printf("%d\n", ans);33 34     return 0;35 }