POJ2187 旋转卡壳+凸包

题意:给定一些点，求最远的点的距离。

凸包+旋转卡壳

/*
旋转卡壳
凸包中的点为顺时针存储
*/
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<algorithm>
#include<iostream>
#include<queue>
//#include<map>
#include<math.h>
using namespace std;
typedef long long ll;
//typedef __int64 int64;
const int maxn = 50005;
const int inf = 0x7fffffff;
struct node{
    int x,y;
    bool operator <( const node &p ) const {
        return y<p.y||(y==p.y&&x<p.x);
    }
};
node pnt[ maxn ],res[ maxn ];
int cross( node sp,node ep,node op ){
     return (sp.x - op.x) * (ep.y - op.y)-(ep.x - op.x) * (sp.y - op.y);
}
/*
ep
|
|
op----sp
( from sp to ep )
*/

int dis2( node a,node b ){
    return (( a.x-b.x )*( a.x-b.x )+( a.y-b.y )*( a.y-b.y ));
}

int graham( int n ){
    int top=1;
    sort( pnt,pnt+n );//!!!!!
    if( n==0 ) return 0;
    else res[ 0 ]=pnt[ 0 ];
    if( n==1 ) return 1;
    else res[ 1 ]=pnt[ 1 ];
    if( n==2 ) return 2;
    else res[ 2 ]=pnt[ 2 ];
    
    for( int i=2;i<n;i++ ){
        while( top>0&&cross( res[ top ],pnt[ i ],res[ top-1 ] )>=0 )
            top--;
        res[ ++top ]=pnt[ i ];
    }
    int tmp=top;
    res[ ++top ]=pnt[ n-2 ];
    for( int i=n-3;i>=0;i-- ){
        while( top!=tmp&&cross( res[ top ],pnt[ i ],res[ top-1 ] )>=0 )
            top--;
        res[ ++top ]=pnt[ i ];
    }
    return top;
}

int rotating( int n ){
    int q=1;
    int ans=0;
    res[ n ]=res[ 0 ];
    for( int i=0;i<n;i++ ){
        while( cross( res[ i ],res[ q+1 ],res[ i+1 ] )>cross( res[ i ],res[ q ],res[ i+1 ] ) )    
            q=(q+1)%n;
        ans=max( ans,max( dis2( res[i],res[q] ),dis2( res[i+1],res[q+1] ) ) );
    }
    return ans;
}
/*
void test(){
    int sum=0;
    node a,b,c;
    a.x=a.y=1;
    b.x=3,b.y=1;
    c.x=1,c.y=7;
    printf("%d\n",cross(a,b,c));
}    
*/
/*
void test2( int cnt ){
    printf("\n");
    for( int i=0;i<cnt;i++ )
        printf("%d %d\n",res[i].x,res[i].y);
    printf("\n");
}
*/
int main(){
    int n;
    //test();
    while( scanf("%d",&n)!=EOF ){
        for( int i=0;i<n;i++ )
            scanf("%d%d",&pnt[ i ].x,&pnt[ i ].y);
        int cnt=graham( n );
        //test2(cnt);
        printf("%d\n",rotating( cnt ));
    }
    return 0;
}