NEXT PALINDROME Runtime Error(SIGSEGV) where did i go wrong,i’cant figure it out pls help

thushar_ke25 · Apr '20

#include<stdio.h>
#include<string.h>
char increment(char ch){
if(ch==‘1’){
ch=‘2’;
return ch;
}
if(ch==‘2’){
ch=‘3’;
return ch;
}
if(ch==‘3’){
ch=‘4’;
return ch;
}
if(ch==‘4’){
ch=‘5’;
return ch;
}
if(ch==‘5’){
ch=‘6’;
return ch;
}
if(ch==‘6’){
ch=‘7’;
return ch;
}
if(ch==‘7’){
ch=‘8’;
return ch;
}
if(ch==‘8’){
ch=‘9’;
return ch;
}
if(ch==‘0’){
ch=‘1’;
return ch;
}

return ch;
}

int main()
{
long int size,i,firstplace=0,changeplace;
long int lowerbound,upperbound;
scanf("%ld",&size);

char str[size][100000];

for( i=0;i<size;i++)
   scanf(" %s",str[i]);

for( i=0;i<size;i++){
   
    if(strlen(str[i])==1){
       
        if(str[i][0]!='9')
        str[i][0]=increment(str[i][0]);
        else{
        str[i][0]='1';
        str[i][1]='1';
        }
       
    }
    
    else if(str[i][ strlen(str[i])-1 ]!='9')
    str[i][strlen(str[i])-1] = increment(str[i][strlen(str[i])-1]);
    
    else if(str[i][ strlen(str[i])-1 ]=='9'){
    	changeplace=strlen(str[i])-1;
    	
    	
    	while(str[i][ changeplace ]=='9'){
    	str[i][changeplace]='0';	
  
    	if(changeplace==0)
    	break;
    	else
    	changeplace--;
    	}
    	
    	if(changeplace!=0)
    	str[i][changeplace]=increment(str[i][changeplace]);
    	else{
    	str[i][0]='1';
    	str[i][strlen(str[i])]='0';
    	str[i][strlen(str[i])+1]='\0';
    	}
    }
    
    
    
    
    
    if(strlen(str[i])>1)
    {
        firstplace=0;
        while(str[i][firstplace]=='0')
        firstplace++;
      
     lowerbound=firstplace;
     upperbound=strlen(str[i])-1;
   
    while( ( lowerbound < upperbound ) && ( lowerbound < (( lowerbound + upperbound )+1)/2-1 ) ){
               str[i][upperbound]=str[i][lowerbound];
               upperbound--;
               lowerbound++;
        }
       
    if((( lowerbound + upperbound )+1)%2==0){
        if( str[i][lowerbound] < str[i][upperbound] ){
            str[i][lowerbound] = increment(str[i][lowerbound]);
            str[i][upperbound] = str[i][lowerbound];
        }
        else
        str[i][upperbound]=str[i][lowerbound];
    }
    else if((( lowerbound + upperbound )+1)%2!=0)
    {
        if(str[i][lowerbound+1]!='9')
        {
            if( str[i][lowerbound] < str[i][upperbound] ){
                str[i][upperbound] = str[i][lowerbound];
                str[i][lowerbound+1] = increment(str[i][lowerbound+1]);
            }
            else
            str[i][upperbound]=str[i][lowerbound];
        }
        else
        {
            if( str[i][lowerbound] < str[i][upperbound] ){
                str[i][lowerbound+1]='0';
                str[i][lowerbound]=increment(str[i][lowerbound]);
                str[i][upperbound]=str[i][lowerbound];
            }
            else
            str[i][upperbound]=str[i][lowerbound];
        }
    }
    }
   
    for(int j=firstplace;j<strlen(str[i]);j++)
    printf("%c",str[i][j]);
    printf("\n");
   
}

return 0;

}

simes · Apr '20

Did you test it with 1 million digit integer? You’ll find the problem if you do.

thushar_ke25 · Apr '20

how can i test it with 1 million integer.
Is it about the time complexity?.

simes · Apr '20

I don’t know how you can do it, but this is how I’d do it:

Open Notepad++, Notepad2 or even Notepad.
Enter the digits 1234567890 - you now have 10 digits.
Select the entire text, copy it, and paste it 9 times. You now have 100 digits.
Select the entire text, copy it, and paste it 9 times. You now have 1000 digits.
Select the entire text, copy it, and paste it 9 times. You now have 10000 digits.
Select the entire text, copy it, and paste it 9 times. You now have 100000 digits.
Select the entire text, copy it, and paste it 9 times. You now have 1000000 digits.
Save this file as palin.in
Compile my program so I get an executable.
Create a .bat file with the command line: palin.exe <palin.in >palin.out
Run the .bat file.

This assumes you’re running on Windows, and have a C++ compiler of course.

thushar_ke25 · Apr '20

thank you simes:smiley:
It worked on ideone an took a time of 0.84sec.
Is the time limit for program less than 0.84 sec?

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simes · Apr '20

Doesn’t ideone have a 64k input limit? That’s too small to show the problem.

edit:

Count the zeros.

thushar_ke25 · Apr '20

Oh sorry didn’t knew that it must have taken the first 64k inputs.
Actually I didn’t understand your process.
If you don’t mind can you tell me where can I learn that.
Thank you.

thushar_ke25 · Apr '20

oh thank you (how foolish of me).
but still showing TLE is it becase of my time complexity or wrong logic.

#include<stdio.h>
#include<string.h>
char increment(char ch){
if(ch==‘1’){
ch=‘2’;
return ch;
}
if(ch==‘2’){
ch=‘3’;
return ch;
}
if(ch==‘3’){
ch=‘4’;
return ch;
}
if(ch==‘4’){
ch=‘5’;
return ch;
}
if(ch==‘5’){
ch=‘6’;
return ch;
}
if(ch==‘6’){
ch=‘7’;
return ch;
}
if(ch==‘7’){
ch=‘8’;
return ch;
}
if(ch==‘8’){
ch=‘9’;
return ch;
}
if(ch==‘0’){
ch=‘1’;
return ch;
}

return ch;
} ;
int main()
{
long int size,i,firstplace=0,changeplace;
long int lowerbound,upperbound;
scanf("%ld",&size);

char str[size][1000000];

for( i=0;i<size;i++)
   scanf(" %s",str[i]);

for( i=0;i<size;i++){
   
    if(strlen(str[i])==1){
       
        if(str[i][0]!='9')
        str[i][0]=increment(str[i][0]);
        else{
        str[i][0]='1';
        str[i][1]='1';
        }
       
    }
   
    else if(str[i][ strlen(str[i])-1 ]!='9')
    str[i][strlen(str[i])-1] = increment(str[i][strlen(str[i])-1]);
   
    else if(str[i][ strlen(str[i])-1 ]=='9'){
    changeplace=strlen(str[i])-1;
   
   
    while(str[i][ changeplace ]=='9'){
    str[i][changeplace]='0';
        if(changeplace==0)
    break;
    else
    changeplace--;
    }
   
    if(changeplace!=0)
    str[i][changeplace]=increment(str[i][changeplace]);
    else{
    str[i][0]='1';
    str[i][strlen(str[i])]='0';
    str[i][strlen(str[i])+1]='\0';
    }
    }
   
   
   
   
   
    if(strlen(str[i])>1)
    {
        firstplace=0;
        while(str[i][firstplace]=='0'){
        if(firstplace<strlen(str[i])-1)
        firstplace++;
        else
        break;
        }
       
     
     lowerbound=firstplace;
     upperbound=strlen(str[i])-1;
   
    while( ( lowerbound < upperbound ) && ( lowerbound < (( lowerbound + upperbound )+1)/2-1 ) ){
               str[i][upperbound]=str[i][lowerbound];
               upperbound--;
               lowerbound++;
        }
       
    if((( lowerbound + upperbound )+1)%2==0){
        if( str[i][lowerbound] < str[i][upperbound] ){
            str[i][lowerbound] = increment(str[i][lowerbound]);
            str[i][upperbound] = str[i][lowerbound];
        }
        else
        str[i][upperbound]=str[i][lowerbound];
    }
    else if((( lowerbound + upperbound )+1)%2!=0)
    {
        if(str[i][lowerbound+1]!='9')
        {
            if( str[i][lowerbound] < str[i][upperbound] ){
                str[i][upperbound] = str[i][lowerbound];
                str[i][lowerbound+1] = increment(str[i][lowerbound+1]);
            }
            else
            str[i][upperbound]=str[i][lowerbound];
        }
        else
        {
            if( str[i][lowerbound] < str[i][upperbound] ){
                str[i][lowerbound+1]='0';
                str[i][lowerbound]=increment(str[i][lowerbound]);
                str[i][upperbound]=str[i][lowerbound];
            }
            else
            str[i][upperbound]=str[i][lowerbound];
        }
    }
    }
   
    for(int j=firstplace;j<strlen(str[i]);j++)
    printf("%c",str[i][j]);
    printf("\n");
   
}

return 0;

}

simes · Apr '20

Edit: this was a reply to your previous post. You posted again as I was writing it.

I’m not totally sure what you mean.

Practice helps. When something doesn’t work as you expect, check the code very carefully. Read through the problem statement again in case you’ve misread anything. Check the constraints, and test the code with the biggest and smallest data allowed. etc etc.

And yes, I’ve fallen foul of all these myself.

simes · Apr '20

ok, in no particular order. And I don’t know how much some of these will affect the speed.

Increment function - why not just ch++?
I’ve seen this a lot - why not read, process, and write one test case at a time? There’s no need to read all test cases first, then process them all, before writing the output. It usually simplifies the code to do one test case at a time, and means the str array would be smaller, possibly a lot smaller since you don’t know how many test cases there are.
strlen. Doesn’t C++ strlen scan the string looking for the terminating null? When the string is a million digits long, that’s gotta take a while right? If you know how long the whole string is, then you also know how long it is when starting from index i.
The % operator is relatively slow, same with divide. When time is tight, avoid them if you can. You can test the bottom bit to determine whether a number is odd or even, rather than use x%2!=0.
Instead of printing one character of the answer at a time, can’t you print it all in one go?
while I’m here, I might as well mention the buffer size again. What about space for the terminating null?
When the integer is 9, what’s the answer? When the integer is 99, what’s the answer? See the pattern? So when the integer is 1 million 9s, how long will the answer be? That’s the buffer size again.

thushar_ke25 · Apr '20

thank you!!
followed your advice and it helped me a alot.
It got accepted. sorry for my silly and foolish doubts.

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