int.pas

   1 var
   2         a:array [0..10000] of longint;
   3         data:array [0..1000,1..2] of longint;
   4         f:array [0..1000] of longint;
   5         n,i,j,max1,maxk1,max2,maxk2,ans,k:longint;
   6
   7 procedure qsort(l,r:longint);
   8 var
   9         i,j,m:longint;
  10
  11 begin
  12         i:=l; j:=r;
  13         m:=data[(l+r) div 2,1];
  14         repeat
  15                 while data[i,1]<m do inc(i);
  16                 while data[j,1]>m do dec(j);
  17                 if i<=j then
  18                         begin
  19                                 data[0]:=data[i]; data[i]:=data[j]; data[j]:=data[0];
  20                                 inc(i); dec(j);
  21                         end;
  22         until i>j;
  23         if l<j then qsort(l,j);
  24         if r>i then qsort(i,r);
  25 end;
  26
  27 begin
  28         readln(n);
  29         for i:=1 to n do readln(data[i,1],data[i,2]);
  30         qsort(1,n);
  31         for i:=1 to n-1 do
  32           if data[i,1]=data[i+1,1] then
  33             begin
  34                 if data[i,2]<data[i+1,2] then
  35                         begin
  36                                 data[i+1,1]:=maxint; data[i+1,2]:=maxint;
  37                         end
  38                 else
  39                         begin
  40                                 data[i,1]:=maxint; data[i,2]:=maxint;
  41                         end;
  42             end;
  43         qsort(1,n);
  44         while data[n,1]=maxint do dec(n);
  45         for i:=1 to n do
  46                 for j:=data[i,1] to data[i,2] do
  47                         inc(a[j]);
  48         fillchar(f,sizeof(f),0);
  49         for i:=1 to n do
  50         begin
  51             if f[i]>=2 then continue;
  52             max1:=a[data[i,1]]; maxk1:=data[i,1];
  53             max2:=a[data[i,2]]; maxk1:=data[i,2];
  54             for k:=data[i,1]+1 to data[i,2]-1 do
  55                     if a[k]>max1 then begin max2:=max1; maxk2:=maxk1; max1:=a[k]; maxk1:=k; end
  56             else if a[k]>max2 then begin max2:=a[k]; maxk2:=k; end;
  57             if f[i]=0 then
  58                 begin
  59                     inc(ans); a[maxk2]:=0;
  60                     j:=i+1;
  61                     while (maxk2>=data[j,1]) and (maxk2<=data[j,2]) do
  62                         begin
  63                             inc(f[j]); inc(j);
  64                         end;
  65                 end;
  66             inc(ans); a[maxk1]:=0;
  67             j:=i+1;
  68             while (maxk1>=data[j,1]) and (maxk1<=data[j,2]) do
  69                 begin
  70                     inc(f[j]); inc(j);
  71                 end;
  72         end;
  73         writeln(ans-1);
  74 end.