24 lines
520 B
C++
24 lines
520 B
C++
#include<cstdio>
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#include<cstring>
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#include<algorithm>
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using namespace std;
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const int maxn=2e6+5;
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int n,a[maxn],Q[maxn],head,tail;
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int main()
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{
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#ifdef local
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freopen("pro.in","r",stdin);
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#endif
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scanf("%d",&n);
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for(int i=1;i<=n;i++) { scanf("%d",&a[i]); a[i+n]=a[i]; }
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int res=0;
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for(int i=1;i<=n*2;i++)
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{
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while(head<tail&&Q[head]<i-n/2) head++;
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if(head<tail) res=max(res,a[i]+i+a[Q[head]]-Q[head]);
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while(head<tail&&a[i]-i>=a[Q[tail-1]]-Q[tail-1]) tail--;
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Q[tail++]=i;
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}
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printf("%d\n",res);
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return 0;
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} |