[计算几何-凸包]pku1113-Wall

题目：没仔细看，只知道是求凸包+圆的面积- -

分析：没啥好分析的。

注：借此题复习了下凸包..发现自己忘得真厉害，尤其是用叉积判断转向..完全弄反了。叉积的时候p1和p2的先后也会影响结果。因为这个小细节郁闷了好久= =

 

糟糕的codes:

 

type point=record x,y:longint; end; var n,l:longint; a:array[0..1000] of point; ans:array[0..1000] of longint; function m(p0,p1,p2:point):longint; var temp:longint; begin temp:=(p1.x-p0.x)*(p2.y-p0.y)-(p2.x-p0.x)*(p1.y-p0.y); if temp>0 then exit(1); if temp<0 then exit(-1); exit(0); end; function comp(x,y:point):boolean; var temp:longint; begin temp:=m(a[0],x,y); if (temp>0) or (temp=0) and (sqr(x.x-a[0].x)+sqr(x.y-a[0].y)<sqr(y.x-a[0].x)+sqr(y.y-a[0].y)) then exit(true) else exit(false); end; procedure swap(var a,b:point); var c:point; begin c:=a; a:=b; b:=c; end; procedure qsort(l,r:longint); var i,j:longint; k:point; begin i:=l; j:=r; k:=a[random(r-l)+l]; while i<=j do begin while comp(a[i],k) do inc(i); while comp(k,a[j]) do dec(j); if i<=j then begin swap(a[i],a[j]); inc(i); dec(j); end; end; if i<r then qsort(i,r); if l<j then qsort(l,j); end; procedure init; var i:longint; begin readln(n,l); randomize; readln(a[0].x,a[0].y); for i:=2 to n do begin with a[i-1] do readln(x,y); if (a[i-1].y<a[0].y) or (a[i-1].y=a[0].y) and (a[i-1].x<a[0].x) then swap(a[0],a[i-1]); end; qsort(1,n-1); end; procedure garham; var i,top:longint; aa:real; begin for i:=1 to 3 do ans[i]:=i-1; top:=3; for i:=3 to n-1 do begin while m(a[ans[top-1]],a[ans[top]],a[i])<0 do dec(top); inc(top); ans[top]:=i; end; aa:=0; for i:=1 to top-1 do aa:=aa+sqrt(sqr(a[ans[i]].x-a[ans[i+1]].x)+sqr(a[ans[i]].y-a[ans[i+1]].y)); aa:=aa+sqrt(sqr(a[ans[top]].x-a[ans[1]].x)+sqr(a[ans[top]].y-a[ans[1]].y)); writeln(round(aa+2*pi*l)); end; begin init; garham; end.

 

PS:听说cppblog的回帖比较多，想转到那，不过用pascal的可以去么= =