很有趣的一道题，题解戳这。
1 #include <iostream> 2 #include <cstdio> 3 #include <cstring> 4 #include <algorithm> 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 ", ans); 33 34 return 0; 35 }