Poj2454 Jersey politics-Greedy + randomization algorithm

When I first read this question, it is clear that everyone has come up with greedy + SEARCH + pruning, but the poj evaluation machine is not powerful, so it must be TLE. So, of course, we know the power of random.

First, verify the correctness of the greedy algorithm:

Policy: sort the N * 3 elements in descending order, and divide the N * 2 elements into two groups. The last n elements are grouped into one group.

Proof: if you do not select this option, the total number of the first two groups will be smaller than the total number of selected groups, which is more likely to fail. Pass.

Randomization algorithm:

Each time an element is selected from the first two sets for exchange, if the conditions are met, the output is directly halt.

I won't prove this randomization.

Code

Program POJ2454;//By_PoetshyConstmaxn=200;Vari,j,k,m,n:Longint;a,rank:Array[1..maxn]of Longint;v:Array[1..maxn]of Boolean;all,sum,temp:Longint;Procedure Qsort(l,r:Longint);var i,j,k,temp:Longint;begini:=l;j:=r;k:=a[(i+j)>>1];repeatwhile a[i]>k do inc(i);while a[j]<k do dec(j);if i<=j thenbegintemp:=a[i];a[i]:=a[j];a[j]:=temp;temp:=rank[i];rank[i]:=rank[j];rank[j]:=temp;inc(i);dec(j);end;until i>j;if i<r then Qsort(i,r);if l<j then Qsort(l,j);end;Procedure Print;var j:Longint;beginfor j:=1 to n do writeln(rank[j]);for j:=n+1 to n*2 do writeln(rank[j]);for j:=n*2+1 to n*3 do writeln(rank[j]);end;Function check:Boolean;beginif sum<=500*n then exit(false);if all-sum<=500*n then exit(false);exit(true);end;BEGINreadln(n);for i:=1 to n*3 dobeginreadln(a[i]);rank[i]:=i;end;Qsort(1,n*3);sum:=0;m:=1;fillchar(v,sizeof(v),0);for i:=1 to n<<1 do inc(all,a[i]);for i:=1 to n do begininc(sum,a[i]);v[i]:=true;end;randomize;while true do beginif Check then beginPrint;halt;end;i:=random(n)+1;j:=random(n)+n+1;inc(sum,a[j]);dec(sum,a[i]);temp:=a[i];a[i]:=a[j];a[j]:=temp;temp:=rank[i];rank[i]:=rank[j];rank[j]:=temp;end;END.