Maximum Value - CodeForces 484 B 水题

B. Maximum Value

time limit per test
1 second

memory limit per test
256 megabytes

input
standard input

output
standard output

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 test(s)

input

3
3 4 5

output

2

题意：找出ai%aj的值的最大值。

思路：排序后从小往大找，假设处理的是a，那么就找比a*2-1，a*3-1，a*4-1...小的最大值。

AC代码如下：

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<cmath>
using namespace std;
typedef long long ll;
int num[2000110],maxn=1000000;
int main()
{
    int T,t,n,m,i,j,k,ans=0;
    scanf("%d",&n);
    for(i=1;i<=n;i++)
    {
        scanf("%d",&k);
        num[k]=k;
    }
    for(i=1;i<=maxn*2+1;i++)
       if(num[i]!=i)
         num[i]=num[i-1];
    for(i=2;i<=maxn;i++)
       if(num[i]==i)
       {
           for(j=i*2;j<=maxn*2+1;j+=i)
           {
               if(num[j-1]>i)
                 ans=max(ans,num[j-1]%i);
           }
       }
    printf("%d\n",ans);
}