[code]poj3349 Snowflake Snow Snowflakes

哈希+挂链。可以用next数组挂链。

const p=99987;
type
  arr=array[1..6]of longint;
var
  a,b:Array[0..200000]of arr;
  next:Array[0..200000]of longint;
  i,j,n,has,tot:longint;

function hash(x:longint):longint;
  var i:longint;
  begin
  hash:=0;
  for i:=1 to 6 do
    hash:=(hash*7+a[x,i]*131) mod p;
  inc(hash);
  end;
function equa(a,b:arr):boolean;
  var i:longint;
  begin
  for i:=1 to 6 do
    if a[i]<>b[i] then exit(false);
  exit(true);
  end ;
procedure sort(var a:arr);
  var i,j,t:longint;
  begin
  for i:=1 to 5 do
    for j:=i to 6 do
      if a[j]>a[i] then
        begin t:=a[j];a[j]:=a[i];a[i]:=t;end;
  end;

begin
  readln(n);
  tot:=p+1;
  for i:=1 to n do
    begin
    for j:=1 to 6 do
      read(a[i,j]);
    sort(a[i]);
    has:=hash(i);
    while (has<>0)and(not equa(b[has],b[200000])) do
      begin
      if equa(b[has],a[i]) then
        begin
        writeln('Twin snowflakes found.');
        halt;
        end;
      has:=next[has];
      end;
    next[has]:=tot+1; inc(tot);
    b[has]:=a[i];
    end;
  writeln('No two snowflakes are alike.');
  end.