CodeForces 484B 数学 Maximum Value

很有趣的一道题，题解戳这。

#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;
}