Problem: There are N integers, A_1, A_2, ..., A_N, written on the blackboard.  You will choose one of them and replace it with an integer of your choice between 1 and 10^9 (inclusive), possibly the same as the integer originally written.  Find the maximum possible greatest common divisor of the N integers on the blackboard after your move.

Submission attempts (in order):
import copy
class SegmentTree():
    __slots__ = ['sz','func','I','seg']
    def __init__(self, N, func, I):
        self.sz = N
        self.func = copy.deepcopy(func)
        self.I = I
        self.seg = [I for i in range(self.sz * 2)]
 
    def assign(self, k, x):
        self.seg[k + self.sz] = x
 
    def build(self):
        for i in range(self.sz - 1, 0, -1):
            self.seg[i] = self.func(self.seg[2 * i], self.seg[2 * i + 1])
 
    def update(self, k, x):
        k += self.sz
        self.seg[k] = x
        while k > 1:
            k //= 2
            self.seg[k] = self.func(self.seg[2 * k], self.seg[2 * k + 1])
 
    def query(self, a, b):
        L = self.I
        R = self.I
        a += self.sz
        b += self.sz
        while a < b:
            if a % 2 == 1:
                L = self.func(L, self.seg[a])
                a += 1
            if b % 2 == 1:
                b -= 1
                R = self.func(self.seg[b], R)
            a //= 2
            b //= 2
        return self.func(L, R)

def main():
    import sys
    read = sys.stdin.buffer.read
    readline = sys.stdin.buffer.readline
    from fractions import gcd
    N = int(readline())
    m = map(int,read().split())
    seg = SegmentTree(N , gcd , 0)
    for i in range(N):
        seg.assign(i , next(m))
    seg.build()
    ans = 1
    for i in range(N):
        ans = max(ans,gcd(seg.query(0,i) , seg.query(i+1,N)))
    print(ans)

main()


import copy
class SegmentTree:
    def __init__(self, N, func, I):
        self.sz = N
        self.func = func
        self.I = I
        self.seg = [I for i in range(self.sz * 2)]
 
    def assign(self, k, x):
        self.seg[k + self.sz] = x
 
    def build(self):
        for i in range(self.sz - 1, 0, -1):
            self.seg[i] = self.func(self.seg[2 * i], self.seg[2 * i + 1])
 
    def update(self, k, x):
        k += self.sz
        self.seg[k] = x
        while k > 1:
            k //= 2
            self.seg[k] = self.func(self.seg[2 * k], self.seg[2 * k + 1])
 
    def query(self, a, b):
        L = self.I
        R = self.I
        a += self.sz
        b += self.sz
        while a < b:
            if a % 2 == 1:
                L = self.func(L, self.seg[a])
                a += 1
            if b % 2 == 1:
                b -= 1
                R = self.func(self.seg[b], R)
            a //= 2
            b //= 2
        return self.func(L, R)

N = int(input())
a = list(map(int,input().split()))
from fractions import gcd
seg = SegmentTree(N , gcd , 0)
for i in range(N):
    seg.assign(i , a[i])
seg.build()
ans = 1
for i in range(N):
    ans = max(ans,gcd(seg.query(0,i) , seg.query(i+1,N)))
print(ans)

import sys
readline = sys.stdin.buffer.readline


class SegmentTree:
    def __init__(self, N, func, I):
        self.sz = 2**(N-1).bit_length()
        self.func = func
        self.I = I
        self.seg = [I] * (self.sz * 2)

    def assign(self, k, x):
        self.seg[k + self.sz] = x

    def build(self):
        for i in reversed(range(1, self.sz)):
            self.seg[i] = self.func(self.seg[2 * i], self.seg[2 * i + 1])

    def update(self, k, x):
        k += self.sz
        self.seg[k] = x
        while k > 1:
            k >>= 1
            self.seg[k] = self.func(self.seg[2 * k], self.seg[2 * k + 1])

    def query(self, a, b):
        L = self.I
        R = self.I
        a += self.sz
        b += self.sz
        while a < b:
            if a & 1:
                L = self.func(L, self.seg[a])
                a += 1
            if b & 1:
                b -= 1
                R = self.func(self.seg[b], R)
            a >>= 1
            b >>= 1
        return self.func(L, R)


def main():
    def gcd(a, b):
        while b:
            a, b = b, a % b
        return a
    N = int(readline())
    L = map(int, readline().split())
    seg = SegmentTree(N, gcd, 0)
    for i, n in enumerate(L):
        seg.assign(i, n)
    seg.build()
    ans = 1
    for i in range(N):
        ans = max(ans, gcd(seg.query(0, i), seg.query(i+1, N)))
    print(ans)


main()


Verdicts: Time Limit Exceeded

Time Limit Exceeded

Accepted