B. Maximum Value
Time Limit: 20 Sec
Memory Limit: 256 MB
题目连接
http://codeforces.com/contest/484/problem/B
Description
You are given a sequence a consisting of n integers. Find the maximum possible value of (integer remainder of ai divided by aj), where 1 ≤ i, j ≤ n and ai ≥ aj.
Input
The first line contains integer n — the length of the sequence (1 ≤ n ≤ 2·105).
The second line contains n space-separated integers ai (1 ≤ ai ≤ 106).
Output
Print the answer to the problem.
Sample Input
3
3 4 5
Sample Output
2
HINT
题意
给你n个数(n<=1e5),每个数(大小<=2*1e6),要求找到最大的ai%aj(ai>aj)
题解:
类似于筛法,对于每个数,我们都筛出他的倍数
ai%aj最大,可以转化为ai*k-aj最小,记录下每个数的倍数的前面的最大的数就好了
代码
#include<iostream> #include<stdio.h> #include<math.h> using namespace std; int pre[4060005]; int main() { int n;scanf("%d",&n); for(int i=1;i<=n;i++) { int x;scanf("%d",&x); pre[x]=x; } for(int i=1;i<=4000005;i++) pre[i]=max(pre[i],pre[i-1]); int ans = 0; int flag = 1; for(int i=1;i<=2000005;i++) { if(pre[i]==i) for(int j=i;j<=2000005;j+=i) ans = max(pre[i+j-1]%i,ans); } printf("%d ",ans); }