[poj][2187][Beauty Contest]

题目：http://poj.org/problem?id=2187

View Code

#include <iostream>

#include <cstdio>

#include <math.h>

#include <cstring>

#include <algorithm>



#define sqr(x) ((x)*(x))

using namespace std;



const double eps = 1e-8;

const int pi = acos(-1.0);

const int N = 500000+10;



int dcmp(double x) {

    if (x < -eps) return -1;

    else return x > eps;

}



struct cpoint {

    double x, y;

    cpoint() {}

    cpoint(double x, double y):x(x),y(y) {}

    cpoint operator + (const cpoint &u) const {

        return cpoint(x + u.x, y + u.y);

    }

    cpoint operator - (const cpoint &u) const {

        return cpoint(x - u.x, y - u.y);

    }

    double operator * (const cpoint &u) const {

        return x * u.y - y * u.x;

    }

    double operator ^ (const cpoint &u) const {

        return x * u.x + y * u.y;

    }

    bool operator == (const cpoint& u) const {

        return dcmp(x - u.x) == 0 && dcmp(y - u.y) == 0;

    }

    bool operator < (const cpoint& u) const {

        if (dcmp(x - u.x)) return x < u.x;

        else return dcmp(y - u.y) < 0;

    }

    double len() {

        return sqrt(x * x + y * y);

    }

    void get() {

        scanf("%lf%lf", &x, &y);

    }

};



double cross(cpoint o, cpoint p, cpoint q) {

    return (p - o) * (q - o);

}



double dot(cpoint o, cpoint p, cpoint q) {

    return (p - o) ^ (q - o);

}



double dissqr(cpoint p, cpoint q) {

    return sqr(p.x - q.x) + sqr(p.y - q.y);

}



cpoint bp;

int PolarCmp(const cpoint &p1, const cpoint &p2) {

    int u = dcmp(cross(bp, p1, p2));

    return u > 0 || (u == 0 && dcmp(dissqr(bp,p1)-dissqr(bp,p2))<0);

}



void graham(cpoint pin[], int n, cpoint ch[], int &m) {

    int i, j, k, u, v;

    memcpy(ch, pin, n * sizeof(cpoint));

    for (i = k = 0; i < n; i++) {

        u = dcmp(ch[i].x - ch[k].x);

        v = dcmp(ch[i].y - ch[k].y);

        if (v < 0 || (v == 0 && u < 0)) k = i;

    }

    bp = ch[k];

    sort(ch, ch + n, PolarCmp);

    n = unique(ch, ch + n) - ch;

    if (n <= 1) {

        m = n; return ;

    }

    if (dcmp(cross(ch[0], ch[1], ch[n-1])) == 0) {

        m = 2, ch[1] = ch[n-1]; return ;

    }

    ch[n++] = ch[0];

    for (i = 1, j = 2; j < n; j++){

        while (i > 0 && dcmp(cross(ch[i-1], ch[i], ch[j])) <= 0) i--;

        ch[++i] = ch[j];

    }

    m = i;

}



double rotating(cpoint cp[], int n){

    int i = 1; double res = 0.0;

    cp[n] = cp[0];

    for (int j = 0; j < n; j++){

        while (dcmp(fabs(cross(cp[i+1], cp[j], cp[j+1]))-

                fabs(cross(cp[i], cp[j], cp[j+1])) ) > 0)

            i = (i + 1) % n;

        res = max(res, max(dissqr(cp[i], cp[j]),

                dissqr(cp[i+1], cp[j+1])));

    }

    return res;

}

cpoint fp[N], ch[N];

int main()

{

    //freopen("D:/a.txt", "r", stdin);

    int n, m;

    while (~scanf("%d", &n))

    {

        for (int i=0; i<n; i++)

            fp[i].get();

        graham(fp, n, ch, m);

        double ans = rotating(ch, m);

        printf("%d\n", (int)(ans+0.5));

    }

    return 0;

}