poj 2187 Beauty Contest 凸包模板+求最远点对

题目链接

题意：给你n个点的坐标，n<=50000,求最远点对

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <vector>
#include <queue>
#include <map>
#include <algorithm>
#include <set>
using namespace std;
#define MM(a) memset(a,0,sizeof(a))
typedef long long ll;
typedef unsigned long long ULL;
const int mod = 1000000007;
const double eps = 1e-10;
const int inf = 0x3f3f3f3f;
const int big=50000;
int max(int a,int b) {return a>b?a:b;};
int min(int a,int b) {return a<b?a:b;};
struct node{
  int x, y;
}ne[50005];
bool cmp(node a,node b)
{
   if(a.x!=b.x)
       return a.x<b.x;
   return a.y<b.y;
}

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

int a[50005],m,k;
void tubao(int n)
{
    sort(ne+1,ne+n+1,cmp);
    m=0;

    for(int i=1;i<=n;i++)
        {
         while(m>=2&&cross(ne[a[m-1]],ne[a[m]],ne[i])<=0)
                m--;
           ++m;
           a[m]=i;
        }
    k=m;
    for(int i=n-1;i>=1;i--)
      {
        while((m>=k+1)&&cross(ne[a[m-1]],ne[a[m]],ne[i])<=0)
                m--;
        ++m;
        a[m]=i;
      }
}

double dist(int i,int j)
{
     return (ne[i].x-ne[j].x)*(ne[i].x-ne[j].x)
     +(ne[i].y-ne[j].y)*(ne[i].y-ne[j].y);
}

int main()
{
    int n;
    while(~scanf("%d",&n))
    {
        for(int i=1;i<=n;i++)
            scanf("%d %d",&ne[i].x,&ne[i].y);
        tubao(n);
        int maxn=0;
        for(int i=1;i<=k;i++)
            for(int j=k+1;j<=m;j++)
              maxn=max(maxn,dist(a[i],a[j]));
        //for(int i=1;i<=m;i++)
          //    cout<<"|||"<<a[i]<<endl;
        printf("%d\n",maxn);
    }
    return 0;
}

　　分析：模板

wa代码：

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <vector>
#include <queue>
#include <map>
#include <algorithm>
#include <set>
using namespace std;
#define MM(a) memset(a,0,sizeof(a))
typedef long long ll;
typedef unsigned long long ULL;
const int mod = 1000000007;
const double eps = 1e-10;
const int inf = 0x3f3f3f3f;
const int big=50000;
int max(int a,int b) {return a>b?a:b;};
int min(int a,int b) {return a<b?a:b;};
struct node{
  int x, y;
}ne[50005];
bool cmp(node a,node b)
{
   if(a.x!=b.x)
       return a.x<b.x;
   return a.y<b.y;
}

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

int a[50005],m;
void tubao(int n)
{
    sort(ne+1,ne+n+1,cmp);
    m=0;

    for(int i=1;i<=n;i++)
        {
           if(m>2&&cross(ne[a[m-1]],ne[a[m]],ne[i])<0)
                m--;
           a[++m]=i;
        }

    for(int i=n-1;i>=1;i--)
      {
        if(i<=(n-2)&&cross(ne[i],ne[a[m]],ne[a[m-1]])>0)
                m--;
        a[++m]=i;
      }
}

double dist(int i,int j)
{
     return (ne[i].x-ne[j].x)*(ne[i].x-ne[j].x)
     +(ne[i].y-ne[j].y)*(ne[i].y-ne[j].y);
}

int main()
{
    int n;
    while(~scanf("%d",&n))
    {
        for(int i=1;i<=n;i++)
            scanf("%d %d",&ne[i].x,&ne[i].y);
        tubao(n);
        int maxn=0;
        for(int i=1;i<=m;i++)
            for(int j=1;j<=m;j++)
              if(i!=j)
              maxn=max(maxn,dist(a[i],a[j]));
        //for(int i=1;i<=m;i++)
          //    cout<<"|||"<<a[i]<<endl;
        printf("%d\n",maxn);
    }
    return 0;
}