高维宇宙 ssl 2552 最大匹配

题目大意

分析

代码

type
arr=record
x,y,w:longint;
next:longint;
end;

var
a:array[1..10000] of arr;
b:array[1..10000] of longint;
v:array[1..30000] of boolean;
f:array[1..10000000] of longint;
st,ls:array[1..30000] of longint;
i,j,k:longint;
n,m,nm:longint;

function find(r:longint):boolean;
var
i,j,k:longint;
begin
find:=true;
i:=ls[r];
while i<>0 do
begin
with a[i] do
if not v[y]
then
begin
k:=st[y]; st[y]:=r; v[y]:=true;
if (k=0) or find(k) then exit;
st[y]:=k;
end;
i:=a[i].next;
end;
find:=false;
end;

procedure main;
var
i,j,k:longint;
z:boolean;
begin
for i:=1 to n do
begin
fillchar(v,sizeof(v),0);
z:=find(i);
end;
end;

begin
readln(n);
nm:=0;
fillchar(a,sizeof(a),false);
for i:=2 to trunc(sqrt(1000000)) do
if f[i]=0
then for j:=2 to 1000000 div i do
f[i*j]:=1;
for i:=1 to n do
read(b[i]);
for i:=1 to n do
for j:=1 to n do
if f[b[i]+b[j]]=0
then begin
nm:=nm+1;
with a[nm] do
begin
x:=i;
y:=j+n;
next:=ls[x];
ls[x]:=nm;
end;
end;
main;
j:=0;
for i:=n+1 to n+n do
if st[i]<>0 then j:=j+1;
write(j div 2);
end.