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;}
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