Codeforces598C（極角排序）

先佔坑

ACcode：

//#pragma comment(linker, "/STACK:1024000000,1024000000")
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<iostream>
#include<vector>
#include<set>
#include<map>
#include<queue>
#include<sstream>
#include<string>
#include<bitset>
using namespace std;

typedef long long LL;
typedef long double lldouble;

const LL LINF = (1LL <<60);
const int INF = 1 << 30;


const int NS = 110000;
const int MS = 19;
const int MOD = 1000000007;
const lldouble eps = 10e-12;
const lldouble PI = acos(-1.0);

struct mpoint
{
    lldouble x, y;
    lldouble angle;
    int id;

    mpoint() {};
    mpoint(lldouble _x, lldouble _y, int _id)
    {
        id = _id;
        x = _x, y = _y;
        angle = getAngle();
    }

    mpoint operator + (const mpoint& _v)const
    {
        return mpoint(x + _v.x, y + _v.y, id);
    }

    mpoint operator - (const mpoint& _v)const
    {
        return mpoint(x - _v.x, y - _v.y, id);
    }

    double operator * (const mpoint& _v)const
    {
        return (x * _v.x + y * _v.y, id);
    }

    lldouble getDistance()
    {
        return sqrt(x * x + y * y);
    }

    bool isequal(lldouble _x, lldouble _y)
    {
        return bool(fabs(_x - _y) < eps);
    }

    bool isequal(const mpoint _v)
    {
        return isequal(x, _v.x) && isequal(y, _v.y);
    }

    bool isequalzero()
    {
        return isequal(mpoint(0.0, 0.0, 0));
    }

    lldouble getAngle()
    {
        lldouble _angle = 0.12345;
        if(isequal(x, 0.0))
        {
            if(y > 0.0)         _angle = 0.5 * PI;
            else if(y < 0.0)    _angle = 1.5 * PI;
            else                _angle = -1.0;
        }
        else
        {
            lldouble det = atan( fabs((lldouble)y / x) );
            if(x > 0.0 && y >= 0.0)         _angle = det;
            else if(x > 0.0 && y < 0.0)     _angle = 2.0 * PI - det;
            else if(x < 0.0 && y >= 0.0)    _angle = PI - det;
            else                            _angle = PI + det;
        }

        /**angle [0, PI * 2]*/
        return _angle;
    }

    bool operator < (const mpoint& _v) const
    {
        return angle < _v.angle;
    }
};

int n;
mpoint p[NS];

int main()
{
#ifndef ONLINE_JUDGE
    freopen("C.in", "r", stdin);
//    freopen("out.txt", "w", stdout);
#endif
    while(~scanf("%d", &n))
    {
        double x, y;
        for(int i = 0; i < n; i++)
        {
            scanf("%lf %lf", &x, &y);
            p[i] = mpoint(x, y, i + 1);
        }
        sort(p, p + n);

        int ans = -1;
        lldouble minv = 111111.0;
        for(int i = 0; i < n; i++)
        {
       //     printf("p[%d](%.0lf, %.0lf) = %.15lf\n", p[i].id, p[i].x, p[i].y, double(p[i].angle));
            int j = (i + 1) % n;

            lldouble det = p[j].angle - p[i].angle;
            if(0 == j) det += 2 * PI;
            if(det < minv)
            {
                minv = det;
                ans = i;
            }
        }

        printf("%d %d\n", p[ans].id, p[(ans + 1) % n].id);
    }
    return 0;
}