UVa 1453 - Squares 旋转卡壳求凸包直径

旋转卡壳求凸包直径。

参考：http://www.cppblog.com/staryjy/archive/2010/09/25/101412.html

 #include <cstdio>
 #include <cmath>
 #include <algorithm>

 using namespace std;

 const int MAXN =  << ;

 struct Point
 {
     int x, y;
     Point( int x = , int y =  ):x(x), y(y) { }
 };

 typedef Point Vector;

 Vector operator+( Vector A, Vector B )       //向量加
 {
     return Vector( A.x + B.x, A.y + B.y );
 }

 Vector operator-( Vector A, Vector B )       //向量减
 {
     return Vector( A.x - B.x, A.y - B.y );
 }

 Vector operator*( Vector A, double p )      //向量数乘
 {
     return Vector( A.x * p, A.y * p );
 }

 Vector operator/( Vector A, double p )      //向量数除
 {
     return Vector( A.x / p, A.y / p );
 }

 bool operator<( const Point& A, const Point& B )   //两点比较
 {
     return A.x < B.x || ( A.x == B.x && A.y < B.y );
 }

 double Cross( Vector A, Vector B )   //向量叉积
 {
     return A.x * B.y - A.y * B.x;
 }

 int ConvexHull( Point *p, int n, Point *ch )
 {
     sort( p, p + n );
     int m = ;
     for ( int i = ; i < n; ++i )
     {
         while ( m >  && Cross( ch[m - ] - ch[m - ], p[i] - ch[m - ] ) <=  ) --m;
         ch[m++] = p[i];
     }

     int k = m;
     for ( int i = n - ; i >= ; --i )
     {
         while ( m > k && Cross( ch[m - ] - ch[m - ], p[i] - ch[m - ] ) <=  ) --m;
         ch[m++] = p[i];
     }

     if ( n >  ) --m;
     return m;
 }

 int dist( Point a, Point b )
 {
     return (a.x - b.x)*(a.x - b.x)+(a.y - b.y)*(a.y - b.y);
 }

 int RotatingCalipers( Point *ch, int n )
 {
     int q = ;
     int ans = ;
     for ( int i = ; i < n; ++i )
     {
         while ( Cross( ch[i + ] - ch[i], ch[q + ] - ch[i] ) > Cross( ch[i + ] - ch[i], ch[q] - ch[i] ) )
             q = ( q +  ) % n;
         ans = max( ans, max( dist( ch[i], ch[q] ), dist( ch[i + ], ch[q + ] ) ) );
     }
     return ans;
 }

 Point read_Point( int x, int y )
 {
     return Point( x, y );
 }

 Point P[MAXN], ch[MAXN];

 int main()
 {
     int T;
     scanf( "%d", &T );
     while ( T-- )
     {
         int N, cnt = ;
         scanf( "%d", &N );
         for ( int i = ; i < N; ++i )
         {
             int x, y, len;
             scanf( "%d%d%d", &x, &y, &len );
             P[cnt++] = read_Point( x, y );
             P[cnt++] = read_Point( x + len, y );
             P[cnt++] = read_Point( x, y + len );
             P[cnt++] = read_Point( x + len, y + len );
         }

         int m = ConvexHull( P, cnt, ch );
         printf("%d\n", RotatingCalipers( ch, m ) );
     }
     return ;
 }