Codeforces 484B Maximum Value

题目传送门：http://codeforces.com/problemset/problem/484/B

题意：一个数列中找出最大的两个元素取模值

解题思路：先对数列排序，然后对每个元素，针对其倍数元素前面一个元素进行计算比较，取最大值即为答案。

AC代码：

#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; }