斜率优化dp，比较裸
注意int64的运算
1 var f,a,q:array[0..2000010] of int64; 2 i,n,h,t:longint; 3 x,y,z:int64; 4 5 function g(j,k:int64):double; 6 var p,q:double; 7 begin 8 p:=2*(f[k]-f[j])+sqr(k)-sqr(j)-k+j; 9 q:=2*(k-j); 10 exit(p/q); 11 end; 12 13 begin 14 readln(n); 15 for i:=1 to n do 16 read(a[i]); 17 h:=0; 18 t:=0; 19 q[0]:=n; 20 f[n]:=a[n]; 21 for i:=n-1 downto 0 do 22 begin 23 while (h<t) and (g(q[h],q[h+1])>i) do inc(h); 24 x:=q[h]; 25 y:=i; 26 z:=(x-y)*(x-y-1); 27 f[i]:=(2*f[q[h]]+z) div 2+a[i]; 28 if i<>0 then 29 begin 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 end; 35 writeln(f[0]); 36 end.
