delete pics to save space

2.1335.cpp

@@ -0,0 +1,51 @@
+#include<cstdio>
+#include<algorithm>
+using namespace std;
+const int maxn=100010;
+int n,r[maxn],left[maxn],right[maxn];
+bool check(int p)
+{
+	int x=r[1],y=p-r[1];
+	left[1]=x;right[1]=0;
+	for(int i=2;i<=n;i++)
+	{
+		if(i&1)
+		{
+			right[i]=min(y-right[i-1],r[i]);
+			left[i]=r[i]-right[i];
+		}
+		else
+		{
+			left[i]=min(x-left[i-1],r[i]);
+			right[i]=r[i]-left[i];
+		}
+	}
+	return left[n]==0;
+}
+int main()
+{
+#ifdef local
+	freopen("pro.in","r",stdin);
+#endif
+	while(scanf("%d",&n)==1&&n)
+	{
+		for(int i=1;i<=n;i++) scanf("%d",&r[i]);
+		if(n==1) { printf("%d\n",r[1]); continue; }
+		r[n+1]=r[1];
+		
+		int L=0,R=0;
+		for(int i=1;i<=n;i++) L=max(L,r[i]+r[i+1]);
+		if(n&1)
+		{
+			for(int i=1;i<=n;i++) R=max(R,r[i]*3);
+			while(L<R)
+			{
+				int M=(L+R)>>1;
+				if(check(M)) R=M;
+				else L=M+1;
+			}
+		}
+		printf("%d\n",L);
+	}
+	return 0;
+}