52 lines
831 B
C++
52 lines
831 B
C++
#include<cstdio>
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#include<algorithm>
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using namespace std;
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const int maxn=100010;
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int n,r[maxn],left[maxn],right[maxn];
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bool check(int p)
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{
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int x=r[1],y=p-r[1];
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left[1]=x;right[1]=0;
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for(int i=2;i<=n;i++)
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{
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if(i&1)
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{
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right[i]=min(y-right[i-1],r[i]);
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left[i]=r[i]-right[i];
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}
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else
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{
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left[i]=min(x-left[i-1],r[i]);
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right[i]=r[i]-left[i];
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}
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}
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return left[n]==0;
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}
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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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while(scanf("%d",&n)==1&&n)
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{
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for(int i=1;i<=n;i++) scanf("%d",&r[i]);
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if(n==1) { printf("%d\n",r[1]); continue; }
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r[n+1]=r[1];
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int L=0,R=0;
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for(int i=1;i<=n;i++) L=max(L,r[i]+r[i+1]);
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if(n&1)
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{
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for(int i=1;i<=n;i++) R=max(R,r[i]*3);
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while(L<R)
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{
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int M=(L+R)>>1;
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if(check(M)) R=M;
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else L=M+1;
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}
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}
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printf("%d\n",L);
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}
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return 0;
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}
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