BOJ - 7420 - 맹독 방벽

import sys
import math

_PI = 3.1415926535

def getDegree(p1, p2):
    return p2[0] - p1[0], p2[1] - p1[1]

def ccw(p1, p2, p3):
    v, u = getDegree(p1, p2), getDegree(p2, p3)
    if v[0] * u[1] > v[1] * u[0]:
        return True
    else: return False

def convex_hull(position):
    convex = []
    for p3 in position:
        while len(convex) >= 2:
            p1, p2 = convex[-2], convex[-1]
            if ccw(p1, p2, p3):
                break
            convex.pop()
        convex.append(p3)
    return convex

def getPointLength(p1, p2):
    return math.sqrt(math.pow(p2[0] - p1[0], 2) + math.pow(p2[1] - p1[1], 2))

def getVector(p1, p2):
    return (p1[0] * p2[0] + p1[1] * p2[1])

def getRadius(p1, p2, p3):
    inner = getVector((p2[0] - p1[0], p2[1] - p1[1]), (p2[0] - p3[0], p2[1] - p3[1]))
    return math.acos(inner / getPointLength(p2, p1) / getPointLength(p2, p3))

def solution():
    N, L = map(int, sys.stdin.readline().split())

    position = []
    for _ in range(N):
        x, y = map(int, sys.stdin.readline().split())
        position.append((x, y))

    position = sorted(position, key=lambda x:(x[0], x[1]))
    ccwtemp = convex_hull(position)
    position.reverse()

    temp = convex_hull(position)
    for i in range(1, len(temp)-1):
        ccwtemp.append(temp[i])

    ret = 0
    length = len(ccwtemp)
    for i in range(len(ccwtemp)):
        ret += getPointLength(ccwtemp[i % length], ccwtemp[(i+1) % length])

    for i in range(len(ccwtemp)):
        theta = getRadius(ccwtemp[(i - 1) % length], ccwtemp[i%length], ccwtemp[(i + 1) % length])
        ret += L * (_PI - theta)

    print(round(ret))

solution()

https://www.acmicpc.net/problem/7420