Educational Codeforces Round 1 C - Nearest vectors

【题意】求n个从原点出发的向量中相距最近的两个的编号

【解题方法】极角排序！

【AC code】

#include <bits/stdc++.h>using namespace std;const int maxn=100010;const double PI=acos(-1);int n;struct Point{    int x,y,id;    long double ang;    void read(){        scanf("%d%d",&x,&y);        ang=atan2(y,x);    }    bool operator<(const Point &p) const{        return ang<p.ang;    }}a[maxn];int main(){    cin>>n;    for(int i=1; i<=n; i++){        a[i].read();        a[i].id=i;    }    sort(a+1,a+n+1);    a[n+1]=a[1];    a[n+1].ang+=2*PI;    long double ang=0x3f3f3f3f;    int id;    for(int i=1; i<=n; i++){        long double now=a[i+1].ang-a[i].ang;        if(ang>now){            ang=now;            id=i;        }    }    printf("%d %d\n",a[id].id,a[id+1].id);}