CodeForces 484B 数学 Maximum Value

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

const int maxn = 200000 + 10;
const int maxm = 1000000 + 10;

int a[maxn], f[maxm];

int main()
{
int n; scanf("%d", &n);
for(int i = 0; i < n; i++) scanf("%d", a + i);
sort(a, a + n);
n = unique(a, a + n) - a;

int M = a[n-1];
for(int i = 0; i < n; i++)
for(int j = a[i] + 1; j <= a[i+1]; j++) f[j] = a[i];

int ans = 0;
for(int i = 0; i < n; i++)
{
for(int j = a[i] * 2; j <= M; j += a[i])
{
ans = max(ans, f[j] % a[i]);
}
ans = max(ans, M % a[i]);
}
printf("%d\n", ans);

return 0;
}