目录

cf598c: Nearest vectors

目录

cf598c: Nearest vectors

极角排序

  • 先把所有点极角排序
  • 然后获得相邻点夹角的表示,取最小
  • 为了避免浮点误差,比较角的大小用叉乘判断
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
import sys
input = lambda: sys.stdin.readline().rstrip()
from math import atan2

def II(base=10):
    return int(input(),base)

def LI():
    return list(map(int,input()))

def LII():
    return list(map(int,input().split()))

def dot(u,v):
    return u[0]*v[0]+u[1]*v[1]

def cross(u,v):
    return u[0]*v[1]-u[1]*v[0]

n = II()
A = [LII() for _ in range(n)]
B = sorted(range(n),key=lambda i: atan2(A[i][1],A[i][0]))
res = [(-1,0),0,0]
for i,j in zip(B,B[1:]+B[:1]):
    u = [dot(A[i],A[j]),abs(cross(A[i],A[j]))]
    if cross(res[0],u)<=0:
        res = [u,i,j]
i,j = res[1:]
print(i+1,j+1)

343 ms