Https://www.codechef.com/viewsolution/27971127 (TRAINSET)

help
1

https://www.codechef.com/viewsolution/27971127

please anyone help in trainset. i think its working fine but codechef is giving WA.

2

There’s a vector index-out-of-bounds at line 30 which might be causing the problem.

2 Likes
3

but in that case sample test cases also should not work. but they are working.

4

No, because it’s Undefined Behaviour so anything can happen, including the program working fine for the sample testcases.

5

ok. I will try another approach.

6

For a concrete testcase that (might) fail, try this:

2
2
a 0
a 0
1
a 0

But as I said, it’s Undefined Behaviour, so anything can happen (though it fails on my machine :))

1 Like
7

https://www.codechef.com/viewsolution/27971508
will you see this one.

8

That doesn’t pass the sample testcase :slight_smile:

As a hint, you were very close with your original submission - you just needed a small amount of code to guard against the index-out-of-bounds.

2 Likes
9

a small off topic question.
I saw your codechef contest graph has always positive slope. How did you manage to reach 6 stars in just 4 months.
How can I improve my skills like yours.

another question: how did you find that

this test case will fail.

1 Like
10

I was doing Hackerrank for a few years before I joined here: https://www.hackerrank.com/ssjgz

Edit: Plus I only do Long Challenges, which are easier in many ways :slight_smile:

I just saw what the flaw in your submission was (the out-of-bounds access) and tried to come up with a testcase that could feasibly exploit it :slight_smile:

3 Likes
11

In case you want the compiler to inform you when there is an attempt to subscript a container with an out-of-bounds index, you may add the -D_GLIBCXX_DEBUG compiler flag.
Credits: @ssjgz
Source: COPRIME3 using Mobius Function - #5 by ssjgz
:slightly_smiling_face:

2 Likes
12

#include <bits/stdc++.h>
using namespace std;
int main(){
int test;
cin>>test;
while(test–){
int n;
cin>>n;
string s[n];
int a[n];
for(int i=0;i<n;i++){
cin>>s[i]>>a[i];
}
int ttl[2];
ttl[0]=0;
ttl[1]=0;
int sum=0;
bool p[n];

for(int i=0;i<n;i++){
if(p[i]==0){

    if(a[i]==0){
     ttl[0]++;
    }else{
    ttl[1]++;
    }

for(int j=i+1;j<n;j++){
        if(p[j]==0){
    if(s[i]==s[j]){
         if(a[j]==0){
     ttl[0]++;
    }else{
    ttl[1]++;
    }
     p[j]=true;
    }
        }
}
    }

sum+=max(ttl[0],ttl[1]);
ttl[0]=0;
ttl[1]=0;

}
cout<<sum<<endl;
}
return 0;
}

why is this giving wa problem TRAINSET.

13

Please either format your code or (better!) link to your submission - the forum software has mangled it and it won’t compile! :slight_smile:

14

https://www.codechef.com/viewsolution/31584195
pls check it out for TRAINSET not getting ac i dont know why

1 Like
15

You need to initialise all elements of b - they’ll contain random values, otherwise.

2 Likes
16

More importantly what is this

for(int i=0;i<n;i++){
        if(p[i]==0){

        if(a[i]==0){
         ttl[0]++;
        }else{
        ttl[1]++;
        }

    for(int j=i+1;j<n;j++){
            if(p[j]==0){
        if(s[i]==s[j]){
             if(a[j]==0){
         ttl[0]++;
        }else{
        ttl[1]++;
        }
         p[j]=true;
        }
            }
    }
        }

    sum+=max(ttl[0],ttl[1]);
    ttl[0]=0;
    ttl[1]=0;

}

Please use better indentation and intuitive variable names. Instead of using so many nested ifs, you can use the && operator, and make sure deeper ifs are indented more, and so are their corresponding curly brackets.

2 Likes