POJ 3787 convex Hull of Lattice Points seeking convex hull

Test instructions

Bare convex bag.

Analysis:

Graham template directly on.

Code:

POJ 3787//sep9#include <iostream> #include <algorithm>using namespace Std;const int maxn=64;struct p{int x , Y;} Pnt[maxn],cnt[maxn];int n;int cmp (P a,p b) {if (A.Y!=B.Y) return A.y<b.y;return a.x<b.x;} int Cross (P a,p b,p c) {int x1=b.x-a.x;int y1=b.y-a.y;int x2=c.x-a.x;int y2=c.y-a.y;return x1*y2-x2*y1;} int Graham () {sort (pnt,pnt+n,cmp); int i,pos=1;cnt[0]=pnt[0];cnt[1]=pnt[1];for (i=2;i<n;++i) {while (pos>0& &cross (Cnt[pos-1],cnt[pos],pnt[i]) <=0)--pos;cnt[++pos]=pnt[i];} int Bak=pos;for (i=n-2;i>=0;--i) {while (Pos>bak&&cross (Cnt[pos-1],cnt[pos],pnt[i]) <=0)--pos;cnt[ ++pos]=pnt[i];} return POS;} int main () {int cases,case_num;scanf ("%d", &cases), while (cases--) {scanf ("%d%d", &case_num,&n); int pos; for (int i=0;i<n;++i) scanf ("%d%d", &pnt[i].x,&pnt[i].y);p rintf ("%d%d\n", Case_num,pos=graham ()); int index=0;for (int i=1;i<pos;++i) if (CNT[I].Y&GT;CNT[INDEX].Y) index=i;else if (cnt[i].y==cnt[index].y&&cnt [I].x<cnt[index].x] index=I;int Mod=pos;while (pos--) {printf ("%d%d\n", cnt[index].x,cnt[index].y);--index;index+=mod;index%=mod;}}  return 0;}

POJ 3787 convex Hull of Lattice Points seeking convex hull