Qiita Teams that are logged in
You are not logged in to any team

Log in to Qiita Team
Community
OrganizationAdvent CalendarQiitadon (β)
Service
Qiita JobsQiita ZineQiita Blog
0
Help us understand the problem. What is going on with this article?
@komkompi

Atcoder ABC125 C - GCD on Blackboard 別解集

More than 1 year has passed since last update.

C問題なのに脅威の水色
ちょっと捻ってるだけでネタが分かれば解けるヤツ

累積GCD

これが正攻法
左から順番にgcdを取っていって記録していく
右からも同様に
あとで各一点に対して記録した左側gcdと右側gcdで仲良しさせる

ruiseki.py
def euclid(a,b):
    a,b=max(a,b),min(a,b)
    if a%b==0:
        return b
    else:
        a,b=b,a%b
        return euclid(a,b)

N=int(input())
A=list(map(int,input().split()))

org_A=A[:]
#左から最大公約数作る右もね
A=A[::-1]
l=[A.pop(-1)]
while A:
    l.append(euclid(l[-1],A.pop(-1)))

A=org_A
r=[A.pop(-1)]
while A:
    r.append(euclid(r[-1],A.pop(-1)))
r=r[::-1]

ans=0
for i in range(N):
    temp=euclid(l[i-1] if i!=0 else r[i+1],r[i+1] if i!=N-1 else l[i-1])
    ans=max(ans,temp)

print(ans)

セグメント木

初実装
あんまり綺麗に書けなかった、、、
これなら各一点に対してlogNで全体のgcdを求め倒すことができる

seg.py
import fractions

N=int(input())

A=list(map(int,input().split()))

M=[2]
while M[-1]<N:
    M.append(M[-1]*2)

A=A+[0]*(M[-1]-len(A))
A=A[::-1]

for i in range(len(A)-1):
    A.append(fractions.gcd(A[2*i],A[2*i+1]))

A=A[::-1]

ans=0
for index in range(len(A)-M[-1],len(A)-M[-1]+N):
    temp=A[index+1] if index%2==1 else A[index-1]
    index=((index-1) if index%2==1 else (index-2))//2

    while index!=0:
        if index%2==1:
            temp=fractions.gcd(temp,A[index+1])
            index=(index-1)//2
        else:
            temp=fractions.gcd(A[index-1],temp)
            index=(index-2)//2
    ans=max(temp,ans)
print(ans)
0
Help us understand the problem. What is going on with this article?
Why not register and get more from Qiita?
  1. We will deliver articles that match you
    By following users and tags, you can catch up information on technical fields that you are interested in as a whole
  2. you can read useful information later efficiently
    By "stocking" the articles you like, you can search right away
komkompi
くま

Comments

No comments
Sign up for free and join this conversation.
Sign Up
If you already have a Qiita account Login
0
Help us understand the problem. What is going on with this article?