B. Maximum Value（Codeforces Round #276(div1)_html/css_WEB-ITnose

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 byaj), 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

33 4 5

output

<strong>找a[i]<a[j]中的a[j]%a[i]的最大值</strong>

<strong>由于ai<1000000;可以hash搞，如果一个点不存在，记录比它小的最大值。</strong>

<strong>至于找最大模后的值，取a[i]==i也就是这个点存在，取模后的最大值肯定i+1+k*i,这样每次增加i查询，</strong>

<strong>查到离最大值最近的值。</strong>

<strong>代码：</strong>

<strong></strong><pre name="code" class="n">#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>using namespace std;const int maxn=2000000+100;int a[maxn];int main(){    int n;    scanf("%d",&n);    int x;    for(int i=0;i<n;i++)    {        scanf("%d",&x);        a[x]=x;    }    for(int i=0;i<maxn;i++)    {        if(a[i]!=i)        a[i]=a[i-1];    }    int ans=0;    for(int i=2;i<maxn;i++)    {        if(a[i]==i)        {            for(int j=i+i-1;j<maxn;j=j+i)            {                if(a[j]%i>ans&&a[j]>i)                ans=a[j]%i;            }        }    }    printf("%d\n",ans);    return 0;}</strong>