Codeforces 484B Maximum Value——思维

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
const int maxn = 2e5+5;
int n, maxa, a[maxn];
int main() {
    scanf("%d", &n);
    maxa = 0;
    for (int i = 1; i <= n; i++) { scanf("%d", &a[i]); maxa = max(maxa, a[i]); }
    n = unique(a+1, a+1+n)-(a+1);
    sort(a+1, a+1+n);
    int ans = 0;
    for (int j = n; j >= 1; j--) {
        if (ans >= a[j]-1) break;
        int temp = a[j];
        while (temp <= maxa) {
            temp += a[j];
            int i = lower_bound(a+1, a+1+n, temp) - a;
            if (i == 1) continue;
            else i--;
            ans = max(ans, a[i] % a[j]);
        }
    }
    printf("%d\n", ans);
    return 0;
}