Server guard coexistence

The meaning of the question is skipped, and the dots on the board are crossed in black and white. The bad point is-1. Then every knight will jump to a different color point on the premise of reasonable jump. We will link the two dots to the edge,

The problem is converted to the largest independent subset problem. The maximum data in Hungary is 0.39 water-over, And the Cena storm stack is used for 9th points, but the direct operation is normal.

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  1 program knight(input,output);  2 type  3    node    = ^link;  4    link    = record  5          goal : longint;  6          next : node;  7       end;        8 var  9    l      : array[0..41000] of node; 10    map      : array[0..201,0..201] of integer; 11    number : array[0..201,0..201] of longint; 12    lk      : array[0..41000] of longint; 13    v      : array[0..41000] of boolean; 14    n,m      : longint; 15 procedure init; 16 var 17    i,j     : longint; 18    sum     : longint; 19    xx,yy : longint; 20 begin 21    readln(n,m); 22    for i:=1 to n*n do 23       l[i]:=nil; 24    map[1,1]:=0; 25    for i:=2 to n do 26       map[1,i]:=1-map[1,i-1]; 27    for i:=2 to n do 28       for j:=1 to n do 29      map[i,j]:=1-map[i-1,j]; 30    sum:=0; 31    for i:=1 to n do 32       for j:=1 to n do 33       begin 34      inc(sum); 35      number[i,j]:=sum; 36       end; 37    for i:=1 to m do 38    begin 39       readln(xx,yy); 40       map[xx,yy]:=-1; 41    end; 42 end; { init } 43 procedure add(x1,y1,x2,y2 : longint ); 44 var 45    tt : node; 46 begin 47    if (x1<1)or(x1>n)or(x2<1)or(x2>n) then 48       exit; 49    if (y1<1)or(y1>n)or(y2<1)or(y2>n) then 50       exit; 51    if (map[x1,y1]=-1)or(map[x2,y2]=-1) then 52       exit; 53    new(tt); 54    tt^.goal:=number[x2,y2]; 55    tt^.next:=l[number[x1,y1]]; 56    l[number[x1,y1]]:=tt; 57 end; { add } 58 procedure make_graph(); 59 var 60    i,j : longint; 61 begin 62    for i:=1 to n do 63       for j:=1 to n do 64      if map[i,j]=0 then 65      begin 66         add(i,j,i-2,j-1); 67         add(i,j,i-1,j-2); 68         add(i,j,i-2,j+1); 69         add(i,j,i-1,j+2); 70         add(i,j,i+1,j-2); 71         add(i,j,i+1,j+2); 72         add(i,j,i+2,j-1); 73         add(i,j,i+2,j+1); 74      end; 75 end; { make_graph } 76 function find(now :longint ):boolean; 77 var 78    t : node; 79 begin 80    t:=l[now]; 81    while t<>nil do 82    begin 83       if not v[t^.goal] then 84       begin 85      v[t^.goal]:=true; 86      if (lk[t^.goal]=0)or(find(lk[t^.goal])) then 87      begin 88         lk[t^.goal]:=now; 89         exit(true); 90      end; 91       end; 92       t:=t^.next; 93    end; 94    exit(false); 95 end; { find } 96 procedure main; 97 var 98    i,j      : longint; 99    answer : longint;100 begin101    answer:=0;102    for i:=1 to n do103       for j:=1 to n do104      if map[i,j]=0 then105      begin106         fillchar(v,sizeof(v),false);107         if find(number[i,j]) then108            inc(answer);109      end;110    writeln(n*n-m-answer);111 end; { main }112 begin113    assign(input,'knight.in');reset(input);114    assign(output,'knight.out');rewrite(output);115    init;116    make_graph;117    main;118    close(input);119    close(output);120 end.