MXLCM prime factors approach giving TLE

general
21

u wont be able to store lcm of array in any datatype since there can conditions where your denominator thats is gcd(a,b) equals 1 when these two are coprimes so u only keep on multiplying which which results in overflow

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22

interger overflow.
suppose all no have gcd 1

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23

But a[i] <= 10^4 and m <= 10^4 so max(lcm) = 10^8 which is within bounds of int and long long.

24

can u explain strip in a tree please

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25

no
try to find the lcm prime numbers example (3,5,7,11) it will be the multiplication of all
and we have a lot of primes under 10^4 so it can easily exceed long long

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26

Oh, I was too dumb. (10^4)^(10^4) would be the upper bound. Thank you for replying, by the way!!!

27
28

have a look at this

29
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please take a look at this

31

Oops! That page doesnā€™t exist or is private.

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32
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33

#include
using namespace std;

long long int gcd(long long int a,long long int b)
{
if (b == 0)
{
return a;
}
return gcd(b, a % b);
}

long long int lcm(long long int a[],long long int n)
{
long long int ans = a[0];

for (long long int i = 1; i < n; i++) 
{
    ans = (a[i] * ans)/ (gcd(a[i], ans)); 
}
return ans;

}

int main() {
// your code goes here
int t;
cin>>t;
while(tā€“)
{
long long int n,m;
cin>>n>>m;

    long long int a[n];
    for(int i=0;i<n;i++)
    {
        cin>>a[i];
    }
    long long int ans=lcm(a,n);
    long long int max=ans;
    long long int num=1;

    for(long long int i=2;i<=m;i++)
    {
        long long int cur=(i*ans)/(gcd(i,ans));
        if(cur>max)
        {
            max=cur;
            num=i;
        }
    }
    cout<<num<<endl;
    
}
return 0;

}
can you help to find the error in this?

34
35

LCM overflows range of int. Store prime factorization instead.

36

have a look here

37

look at this

38

here take a look at this please

39

beautiful approach,i must say!

2 Likes
40

Thank you, till now i got the point but now how will you find the smallest noā€¦ I guess your approach should be traverse from 1 to m and for each no. find the prime factors and multiply with original lcm ???

1 Like