delete pics to save space

p.CH5501.cpp

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