Codeforces 484B Maximum Value

題目傳送門：http://codeforces.com/problemset/problem/484/B

題意：一個數列中找出最大的兩個元素模數值

解題思路：先對數列排序，然後對每個元素，針對其倍數元素前面一個元素進行計算比較，取最大值即為答案。

AC代碼：

#include<cstdio>#include<algorithm>using namespace std;const int maxn = 200005;int num[maxn];int main(){    int n;    scanf("%d", &n);    for (int i = 0; i < n; i++)    {        scanf("%d", &num[i]);    }    sort(num,num+n);    int ans = 0;    for (int i = 0; i < n; i++)    {        if (i && num[i] == num[i-1]) continue;        int k = 2 * num[i];        while (k <= num[n-1])        {            int pos = lower_bound(num,num+n,k) - num;            ans = max(ans,num[pos-1]%num[i]);            k += num[i];        }        ans = max(ans,num[n-1]%num[i]);    }    printf("%d\n",ans);    return 0;}