POJ 2079 Triangle convex bag + rotating jam

Test instructions

For n points on a plane, the maximum triangular area of the n points is obtained.

Analysis:

Rotating jam, but to pay attention to the difference between the most distant point of the plane, the largest triangle of the edge is not necessarily on the convex hull, but also posted in the previously written to find the plane the furthest point of the POJ 2187 code as a comparison.

Code:

POJ 2079//sep9#include <iostream> #include <algorithm> using namespace std;    const int maxn=50012;      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 () {while (scanf ("%d", &n) ==1&&n!=-1) {for (int i=0;i<n;++i) scanf ("%d%d", &pnt[i]. x,&pnt[i].y);              int Pos=graham (); int Ans=0,p=1,i,j,k;for (i=j=k=0;i<pos;++i) {while (ABS (Cross (cnt[i],cnt[j],cnt[(k+1)%pos)) >abs (Cross (cnt[i ],CNT[J],CNT[K])) k= (k+1)%pos;while (ABS (Cross (cnt[i],cnt[(j+1)%pos],cnt[k)) >abs (Cross (CNT[I],CNT[J],CNT[K)        )) j= (j+1)%pos;ans=max (Ans,abs (Cross (cnt[i],cnt[j],cnt[k)));}      printf ("%.2lf\n", ans/2.0);}     return 0;    }

The code that asks for the farthest point pair:

POJ 2187//sep9#include<iostream> #include <algorithm>using namespace std;struct point{int x, y;} Points[50012],bag[50012];int Cross (Point p1,point p2,point p0) {return (p1.x-p0.x) * (P2.Y-P0.Y)-(p2.x-p0.x) * ( P1.Y-P0.Y);} int CMP (point A,point B) {return a.y==b.y?a.x<b.x:a.y<b.y;} int dis (point a,point b) {return (a.x-b.x) * (a.x-b.x) + (A.Y-B.Y) * (A.Y-B.Y);}    int Getbag (point p[],int n,point bag[]) {int i,bp=1; Bag[0]=p[0];bag[1]=p[1];for (I=2;i<n;++i) {while (Bp&&cross (BAG[BP-1],P[I],BAG[BP]) <=0)--bp;bag[++ Bp]=p[i];} int Len=bp;bag[++bp]=p[n-2];for (i=n-3;i>=0;--i) {while (Bp>len&&cross (BAG[BP-1],P[I],BAG[BP]) <=0 )--bp;bag[++bp]=p[i];} return BP;} int main () {int p,i,n;while (scanf ("%d", &n) ==1) {for (i=0;i<n;++i) scanf ("%d%d", &points[i].x,&points[i ].Y), sort (points,points+n,cmp), int dif,ans=0,m=getbag (points,n,bag);p =1;for (i=0;i<m;++i) {while (ABS (Cross (bag [i],bag[i+1],bag[p+1]) >abs (Cross (bag[i],bag[i+1],bag[p))) p= (p+1)%m;ans=max (Ans,max (Dis (bag[I],BAG[P]), DIS (bag[i+1],bag[p+1]));} printf ("%d\n", ans);}}

POJ 2079 Triangle convex bag + rotating jam