【BZOJ1237】配对（贪心，DP）

题意：有n个a[i]和b[i]，调整顺序使abs(a[i]-b[i])之和最小，但a[i]<>b[i]。保证所有 Ai各不相同，Bi也各不相同。

30%的数据满足：n <= 104 100%的数据满足：1 <= n <= 105，Ai和Bi均为1到106之间的整数。

思路：可以证明调整范围一定在三个数以内

 var dp:array[..]of int64;
     a,b,c:array[..]of longint;
     n,i:longint;

 function clac(x,y:longint):int64;
 begin
  if a[x]=b[y] then exit(<<)
   else exit(abs(a[x]-b[y]));
 end;

 procedure swap(var x,y:longint);
 var t:longint;
 begin
  t:=x; x:=y; y:=t;
 end;

 function min(x,y:int64):int64;
 begin
  if x<y then exit(x);
  exit(y);
 end;

 procedure qsort(l,r:longint);
 var i,j,mid:longint;
 begin
  i:=l; j:=r; mid:=c[(l+r)>>];
  repeat
   while mid>c[i] do inc(i);
   while mid<c[j] do dec(j);
   if i<=j then
   begin
    swap(c[i],c[j]);
    inc(i); dec(j);
   end;
  until i>j;
  if l<j then qsort(l,j);
  if i<r then qsort(i,r);
 end;

 begin
  assign(input,'bzoj1237.in'); reset(input);
  assign(output,'bzoj1237.out'); rewrite(output);
  readln(n);
  for i:= to n do read(a[i],b[i]);
  for i:= to n do c[i]:=a[i];
  qsort(,n);
  for i:= to n do a[i]:=c[i];
  for i:= to n do c[i]:=b[i];
  qsort(,n);
  for i:= to n do b[i]:=c[i];
  dp[]:=clac(,);
  dp[]:=min(clac(,)+clac(,),dp[]+clac(,));
  for i:= to n do
  begin
   dp[i]:=<<;
   dp[i]:=min(dp[i],dp[i-]+clac(i,i));
   dp[i]:=min(dp[i],dp[i-]+clac(i,i-)+clac(i-,i));
   dp[i]:=min(dp[i],dp[i-]+clac(i-,i)+clac(i-,i-)+clac(i,i-));
   dp[i]:=min(dp[i],dp[i-]+clac(i-,i-)+clac(i-,i)+clac(i,i-));
   dp[i]:=min(dp[i],dp[i-]+clac(i-,i)+clac(i-,i-)+clac(i,i-));
  end;
  if dp[n]>(<<) then writeln(-)
   else writeln(dp[n]);
  close(input);
  close(output);
 end.