[中山市选] 序列

直接上代码

program seq;constmaxn=100000+10;var    a,f,g,f1,f2:array[0..maxn]of int64;    i,j,n:longint; ans:int64;function max(i,j:int64):int64;begin    if i>j then exit(i); exit(j);end;function min(i,j:int64):int64;begin    if i<j then exit(i); exit(j);end;begin    readln(n); for i:=1 to n do read(a[i]);    for i:=2 to n-1 do f[i]:=f[i-1]+max(0,a[i-1]-a[i]+1);    for i:=n-1 downto 2 do g[i]:=g[i+1]+max(0,a[i+1]-a[i]+1);    j:=2;    for i:=3 to n-2 do beginwhile (j<i-1)and(max(f[j+1]-f[1],g[j+1]-g[i])<=max(f[j]-f[1],g[j]-g[i])) do inc(j);f1[i]:=max(f[j]-f[1],g[j]-g[i]);    end;    j:=n-1;    for i:=n-2 downto 3 do beginwhile (j>i+1)and(max(f[j-1]-f[i],g[j-1]-g[n])<=max(f[j]-f[i],g[j]-g[n])) do dec(j);f2[i]:=max(f[j]-f[i],g[j]-g[n]);    end;    ans:=f1[3]+f2[3];    for i:=3 to n-2 do ans:=min(ans,f1[i]+f2[i]);    writeln(ans);end.