### PARTHO_DAS's blog

By PARTHO_DAS, 15 months ago,

I would like you to read the full story and give me some feedback on it, Thank You.

Today I was solving this amazing 715A - Plus and Square Root problem. After finding the idea and implementing it in C++, I submitted it in C++17 and later in C++20.

But I was getting the wrong answers in the main test 5. At first, I thought my idea was wrong and I tried to prove my idea. Thinking about the problem the whole day I got nothing wrong with my approach and implementation.

By not finding any other way I opened my submission and then I saw the reasons for the wrong answer 198441320. But in theory and my implementation method, there could not have errors such as this.

After that, I got experimental and tested the code, and changed certain bits. But whatever I did it didn't change the verdict.

The main part of my code was:

ll lcm(ll a, ll b){
ll LCM = (a * b);
return LCM;
}
void solve(){

ll n;
scl(n); // scan in long long

ll LCM = 2;

for(int i = 1; i <= n; i++){
ll templcm = lcm(i, i + 1);
ll res = (templcm - LCM) / i + (templcm / i) * (templcm - 1);
cout << res << endl;
LCM = templcm;
}
return;
}


But after that, I submitted the same code with the change of variable type of i (loop Variable) that got AC 198513530.

// Previous codes are unchanged

for(ll i = 1; i <= n; i++){
ll templcm = lcm(i, i + 1);
ll res = (templcm - LCM) / i + (templcm / i) * (templcm - 1);
cout << res << endl;
LCM = templcm;
}


Here I should not have got this verdict because in whatever the type of i (loop Variable) be, it should be converted to long long.

Now I was having fun, in another version: I have declared another variable j, and did this and that also got an AC:

 for(int i = 1; i <= n; i++){
ll templcm = lcm(i, (i + 1) ), templcm2 = lcm(j, j + 1);
templcm = templcm2;
ll res = (templcm - LCM) / i + (templcm / i) * (templcm - 1);
if(templcm != templcm2){
cout << templcm << " " << templcm2 << endl;
}
cout << res << endl;
LCM = templcm;
j++;
}


Finally, I submitted my first submission (Where i in int type) 198505674 in C++14 and with the help of magic it got AC That same code that got WA in C++ 17 and C++20 got AC in C++14.

• +8

By PARTHO_DAS, 2 years ago,

Hi, I really wanna thank Codeforces in short.

I live in Bangladesh. In my county, COVID-19 hit around Jan-2020. Our college and every educational institution were closed for around 1.5 years. My life felt purposeless and dull.I had nothing to do. Time become frozen and felt like a day doesn't pass.

The entertainment become predictable, Nothing new was released. At that time I just saw one site become a part of my life. Like my morning coffee.

That site was not slowing down its activities and I saw it becoming more popular. The site I am talking about you already guessed it, Yes Codeforces.

I have invested time to solve problems and learn new things from this site. When I think about this site, I think how much effort is given to this site by some awesome volunteers.

I just become amazed and the best part of this site is, it is Free. I am especially thankful to MikeMirzayanov for this platform God Bless You.

Thank you Codeforces Team. I am grateful to you and wish you all "Happy New Year" in Advance.

• +354

By PARTHO_DAS, 3 years ago,

Hi there,

After getting Accepted to Timofey and a tree problem with DSU. I found that my solution was wrong.

My approach: In DSU I kept a vertex X in Group D if vertex X has the same color as parents of group D and there is an edge between X and some vertex of group D.

Now for calculating the result. I was iterating over every vertex. In every iteration, I visited over his adjacent vertices and kept count of their group size. After vising, if the count is equal to n — 1 then I say this is my answer and return.

If I could not get any answer then I say there is no answer.

The Main Problem: In the iteration of every vertex. I count for the same group many times for different adjaecnt vertex. So, if the counter becomes n — 1 and found an answer that an error.

This is my Wrong Accepted solution 121082526

The Hack Case:

10
1 5
1 2
3 6
3 9
3 4
4 5
6 7
7 8
9 10
2 2 1 1 2 1 2 2 1 2


For this data, The output should be NO. But My output is

YES
3


But here is another 121055514 solution which giving output NO.

So, here are two different solutions giving different outputs for the same valid input.

MikeMirzayanov Could you please check this.

• +4

By PARTHO_DAS, history, 4 years ago,
I am trying to solve [E. Little Elephant and Inversions](https://codeforces.com/contest/220/problem/E)
But in the third test case :
7 3
1 7 6 4 9 5 3
The expected output is: 6
But I can't understand how it's possible, in my logic I find the answer is: 15

7 3
1 7 6 4 9 5 3
-------------
0 1 2 3 4 5 6 // i
I find :
5 3       || l = 5, r = 6
9 5 3     || l = 4, r = 6
9 5       || l = 4, r = 5
4 9 5     || l = 3, r = 5
4 9       || l = 3, r = 4
6 4 9 5   || l = 2, r = 5
6 4 9     || l = 2, r = 4
6 4       || l = 2, r = 3
7 6 4 9   || l = 1, r = 4
7 6 4     || l = 1, 4 = 3
7 6       || l = 1, r = 2
1 7 6 4 9 || l = 0, r = 4
1 7 6 4   || l = 0, r = 3
1 7 6     || l = 0, r = 2
1 7       || l = 0, r = 1
----------------------------
15 unique l and r, where inversions count is less than or equal to 3.

[My submission](https://codeforces.com/contest/220/submission/96186615)

• +2

By PARTHO_DAS, history, 5 years ago,

I am a noob programmer but my I accepted a problem in CF global round 5. But in the main test got no verdict at that problem then I clicked on my profile submission and I saw runtime error in case no: 1 how this is possible? It comes runtime error in CF in the main test case 1 but in but pretest it was fine in pre-test. it also works fine in ideone. problem link https://codeforces.com/contest/1237/problem/B?statementsLocale=en my solution. https://ideone.com/prrXp7

• +11