CHARGES - Editorial

makasam · June 2, 2021, 7:23am

#include
using namespace std;

int main() {
int x,a,b,c,d,y,z;
string s;
cin >> x;
for(int i=0;i<x;i++)
{
cin>>a>>b;
char arr[a-1];
char k;
int jar[a-1];
cin>>s;
for(int j=0;j<a;j++){
arr[j]=s[j];
k=arr[j];
jar[j] = (int)k;
}
for(int lo=0;lo<b;lo++){
cin>>d;
if(jar[d-1]==0)
{
jar[d-1]=1;
}
else
{
jar[d-1]=0;
}
int dis=0;
for(int ll=1;ll<a;ll++){
if(jar[ll]-jar[ll-1]==0){
dis=dis+1;
}
else{
dis=dis+2;
}
}
cout<<dis<<endl;
}
}

return 0;

}
@darshancool25 can you tell me what is the problem if I code it this way
and why the submission has errors
It will be very kind of you.Thank you.

ssjgz · June 2, 2021, 7:43am

This has out-of-bounds accesses with the sample test input:

[simon@simon-laptop][08:42:22]
[~/devel/hackerrank/otherpeoples]>./compile-latest-cpp.sh 
Compiling makasam-CHARGES.cpp
+ g++ -std=c++14 makasam-CHARGES.cpp -O3 -g3 -Wall -Wextra -Wconversion -DONLINE_JUDGE -D_GLIBCXX_DEBUG -fsanitize=undefined -ftrapv
makasam-CHARGES.cpp: In function ‘int main()’:
makasam-CHARGES.cpp:5:15: warning: unused variable ‘c’ [-Wunused-variable]
     int x,a,b,c,d,y,z;
               ^
makasam-CHARGES.cpp:5:19: warning: unused variable ‘y’ [-Wunused-variable]
     int x,a,b,c,d,y,z;
                   ^
makasam-CHARGES.cpp:5:21: warning: unused variable ‘z’ [-Wunused-variable]
     int x,a,b,c,d,y,z;
                     ^
+ set +x
Successful
[simon@simon-laptop][08:42:28]
[~/devel/hackerrank/otherpeoples]>echo "1
3 3
010
2 1 3" | ./a.out
makasam-CHARGES.cpp:16:18: runtime error: index 2 out of bounds for type 'char [*]'
makasam-CHARGES.cpp:17:20: runtime error: index 2 out of bounds for type 'char [*]'
makasam-CHARGES.cpp:18:18: runtime error: index 2 out of bounds for type 'int [*]'
makasam-CHARGES.cpp:32:26: runtime error: index 2 out of bounds for type 'int [*]'
4
3
makasam-CHARGES.cpp:22:23: runtime error: index 2 out of bounds for type 'int [*]'
makasam-CHARGES.cpp:28:24: runtime error: index 2 out of bounds for type 'int [*]'
2

darshancool25 · June 2, 2021, 7:54am

Everything ssjgz has written is true. I would just like to add few points :

If you ever need to convert a single character (my_char) to its corresponding int value, heres an example : int int_val = my_char - '0';
Note that type casting int_val = (int)(my_char) wont work !!
In your code after each of the k changes, you are recalculating the answer from scratch again (which is quite unnecessary and slow). I suggest have a look at the video editorial for understanding a better approach.

anon38811231 · June 2, 2021, 8:48am

Woah thanks this corner case just didn’t come to my mind , how do you find such corner cases?
Edit: I changed the case when n==1 to output it 0 and continue then too it is giving WA

ssjgz · June 2, 2021, 8:57am

The usual way - simple brute-force solution plus randomised testcase generator

Please link to your most recent WA solution.

anon38811231 · June 2, 2021, 9:11am

https://www.codechef.com/viewsolution/47333753

ssjgz · June 2, 2021, 9:43am

That doesn’t pass the sample test input Pay attention to compiler warnings!

[simon@simon-laptop][10:43:08]
[~/tmp/DONTSYNC/hackerrank/otherpeoples]>./compile-latest-cpp.sh 
Compiling mickey_03-CHARGES.cpp
+ g++ -std=c++14 mickey_03-CHARGES.cpp -O3 -g3 -Wall -Wextra -Wconversion -DONLINE_JUDGE -D_GLIBCXX_DEBUG -fsanitize=undefined -ftrapv
mickey_03-CHARGES.cpp: In function ‘int main()’:
mickey_03-CHARGES.cpp:38:13: warning: this ‘if’ clause does not guard... [-Wmisleading-indentation]
             if(n==1) cout<<"0\n"; continue;
             ^~
mickey_03-CHARGES.cpp:38:35: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the ‘if’
             if(n==1) cout<<"0\n"; continue;
                                   ^~~~~~~~
+ set +x
Successful
[simon@simon-laptop][10:43:18]
[~/tmp/DONTSYNC/hackerrank/otherpeoples]>echo "1                 
3 3
010
2 1 3" | ./a.out

coder0687 · June 2, 2021, 10:00am

Very Simple Code: Link

aadarshsinha · June 2, 2021, 10:55am

Can you please🙏 tell me which test case am i missing . I have tried all including n=1 ,but still WA
link : CodeChef: Practical coding for everyone

ssjgz · June 2, 2021, 11:02am

Already told you

Fix the out-of-bounds access.

anon38811231 · June 2, 2021, 12:09pm

Ohh yess I tried to do it in one line but should have put in curly braces, thanks for your help got AC!
But I did’nt get any compiler warnings as such when I executed that…

aadarshsinha · June 2, 2021, 1:54pm

I just removed the void solve() and placed all the code inside main .Now i am getting correct answer . Can you please tell me why is it so? what wrong in using another function ?

ssjgz · June 2, 2021, 2:00pm

Your AC solution still has the out-of-bounds access:

[simon@simon-laptop][14:59:27]
[~/devel/hackerrank/otherpeoples]>./codechef-download-solution.rb https://www.codechef.com/viewsolution/47337805
Solution written to: aadarshsinha-CHARGES.cpp
[simon@simon-laptop][14:59:37]
[~/devel/hackerrank/otherpeoples]>./compile-latest-cpp.sh                                                       
Compiling aadarshsinha-CHARGES.cpp
+ g++ -std=c++14 aadarshsinha-CHARGES.cpp -O3 -g3 -Wall -Wextra -Wconversion -DONLINE_JUDGE -D_GLIBCXX_DEBUG -fsanitize=undefined -ftrapv
+ set +x
Successful
[simon@simon-laptop][14:59:40]
[~/devel/hackerrank/otherpeoples]>echo "1                                                                       
1 1
0
1" | ./a.out
aadarshsinha-CHARGES.cpp:38:42: runtime error: index 1 out of bounds for type 'char [*]'
aadarshsinha-CHARGES.cpp:39:47: runtime error: index 1 out of bounds for type 'char [*]'
0

so you got lucky.

aadarshsinha · June 2, 2021, 2:26pm

But i am still confused , when i used void solve() function and write the code there it give me wrong answer and when i write the entire code inside main function it gives my correct answer .Why is it so ?
using void solve() : Solution: 47336440 | CodeChef
without viod solve() : Solution: 47341451 | CodeChef

ssjgz · June 2, 2021, 2:27pm

There’s Undefined Behaviour for you

aadarshsinha · June 2, 2021, 2:29pm

okay , thank you so much for helping me out .

arjav_jain · June 2, 2021, 5:17pm

CodeChef: Practical coding for everyone pls help with why this is WAing

ssjgz · June 2, 2021, 5:20pm

Out of bounds access on sample testcase:

[simon@simon-laptop][18:19:24]
[~/devel/hackerrank/otherpeoples]>./compile-latest-cpp.sh 
Compiling arjav_jain-CHARGES.cpp
+ g++ -std=c++14 arjav_jain-CHARGES.cpp -O3 -g3 -Wall -Wextra -Wconversion -DONLINE_JUDGE -D_GLIBCXX_DEBUG -fsanitize=undefined -ftrapv
+ set +x
Successful
[simon@simon-laptop][18:19:28]
[~/devel/hackerrank/otherpeoples]>echo "1
3 3
010
2 1 3
" | ./a.out
/usr/include/c++/7/bits/basic_string.h:1057: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::reference std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator[](std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::reference = char&; std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type = long unsigned int]: Assertion '__pos <= size()' failed.
Aborted (core dumped)

ikshul130 · June 2, 2021, 7:27pm

Can someone please tell what is wrong with my code?
https://www.codechef.com/viewsolution/47349723
I am getting RE (SIGSEGV) error

ssjgz · June 2, 2021, 7:30pm

Exactly the same mistake as this guy: CHARGES - Editorial - #77 by ssjgz