JSOI建筑抢修 （贪心+堆）

Program XJOI2320;
const maxn=150008;
var a,b,f:array[0..maxn] of longint;
    n,i:longint;
    sum,num,ans:int64;
    procedure sort(l,r: longint);
      var
         i,j,x,y: longint;
      begin
         i:=l;
         j:=r;
         x:=b[(l+r) div 2];
         repeat
           while b[i]<x do
            inc(i);
           while x<b[j] do
            dec(j);
           if not(i>j) then
             begin
                y:=a[i];
                a[i]:=a[j];
                a[j]:=y;

                y:=b[i];
                b[i]:=b[j];
                b[j]:=y;
                inc(i);
                j:=j-1;
             end;
         until i>j;
         if l<j then
           sort(l,j);
         if i<r then
           sort(i,r);
      end;
procedure swap(a,b:longint);
var temp:longint;
begin
    temp:=f[a]; f[a]:=f[b];f[b]:=temp;
end;
procedure insert(x:longint);
var i:longint;
begin
    inc(num);
    f[num]:=x;
    i:=num;
    while i>1 do
    begin
        if f[i]>f[i div 2] then swap(i,i div 2) else break;
        i:=i div 2;
    end;
end;
procedure delete(x:longint);
var i:longint;
begin
    f[1]:=f[num];
    dec(num);
    i:=2;
    while i<=num do
    begin
        if (i+1<=num) and (f[i+1]>f[i]) then inc(i);
        if f[i]>f[i div 2] then swap(i,i div 2) else break;
        i:=i*2;
    end;
end;
begin
    readln(n);
    for i:=1 to n do readln(a[i],b[i]);
    sort(1,n);
    sum:=0; num:=0; ans:=0;
    for i:=1 to n do
        if sum+a[i]<=b[i] then
        begin
            inc(ans);
            sum:=sum+a[i];
            insert(a[i]);
        end else
        if a[i]<f[1] then
        begin
            sum:=sum-f[1];
            delete(1);
            insert(a[i]);
            sum:=sum+a[i];
        end;    
    writeln(ans);
end.