练一下斜率优化

 1 var s1,s2,f:array[0..1000010] of int64;
 2     q,a,b:array[0..1000010] of longint;
 3     i,n,h,t,j:longint;
 4 
 5 function g(j,k:longint):double;
 6   var a,b:double;
 7   begin
 8     a:=f[j]-f[k]-s2[j]+s2[k];
 9     b:=s1[k]-s1[j];
10     exit(a/b);
11   end;
12 
13 begin
14   readln(n);
15   for i:=1 to n do
16     read(a[i]);
17   for i:=1 to n do
18   begin
19     read(b[i]);
20     s1[i]:=s1[i-1]+b[i];
21     s2[i]:=s2[i-1]+int64(b[i])*int64(n-i+1);
22   end;
23   h:=0;
24   t:=0;
25   for i:=1 to n do
26   begin
27     while (h<t) and (g(q[h],q[h+1])>=n-i+1) do inc(h);
28     j:=q[h];
29     f[i]:=f[j]+a[i]+s2[i-1]-s2[j]-(s1[i-1]-s1[j])*int64(n-i+1);
30     while (h<t) and (g(q[t],i)>=g(q[t-1],q[t])) do dec(t);
31     inc(t);
32     q[t]:=i;
33   end;
34   writeln(f[n]);
35 end.
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posted on 2015-01-16 22:11  acphile  阅读(107)  评论(0编辑  收藏  举报