Why this program doesn't give right result when used with large strings?

Question

This program takes an input of number of strings followed by the actual strings. The output should be the number of common characters to all strings.

The constraints are:

No of strings <= 100
Length of string <= 100

For example..

Input:

3 abc bcd cde

Output:

1

As only c is common to all strings.

It gives right output when used with small inputs.

But when used with large strings like this :https://hr-testcases.s3.amazonaws.com/2223/input19.txt?AWSAccessKeyId=AKIAINGOTNJCTGAUP7NA&Expires=1408959130&Signature=E%2BMnR6MA0gQNkuWHMvc70eCL5Dw%3D&response-content-type=text%2Fplain

It gives wrong output of 58 instead of 19.

This is my code :

#include<stdio.h>
#include<string.h> 

void main(){
    int n,i,j,count=0;
    char s[100][100];
    scanf("%d",&n);
    for(i=0;i<n;i++){
        scanf("%s",s[i]);
    }
    int t;
    int l = strlen(s[0]);
    for(i=0;i<l;i++){
        t=0;
        for(j=1;j<n;j++){
            if(strchr(s[j],s[0][i])!='\0'){
                t++;
            }
        }
        if(t==n-1)
            count++;
    }
    printf("%d",count);
}

I am doing this question in a site and it is showing right ans as 19. Also if I run this program http://hackerranksol.blogspot.in/2014/05/gem-stones-problem-statement-john-has.html it gives 19 as a answer — SomeDevloperName, Aug 25 '14 at 09:14
@PaulR: not for me in this case: `gcc` with `-Wall` and `-pedantic` only warns about `main` and the mixed declarations and code. Does your compiler tell you more? — Jongware, Aug 25 '14 at 09:20
1) you forgot to allow space for the null terminator 2) you don't process [repeated characters](http://ideone.com/7toUJ5) correctly. — n. m. could be an AI, Aug 25 '14 at 09:21
Possibly some of strings are exactly 100 chars long. What happens then in your `s` array to the long string's terminating NUL char? — CiaPan, Aug 25 '14 at 09:21
@Jongware: I think you're replying to a comment that I had posted in error and had already deleted? — Paul R, Aug 25 '14 at 09:22

score 0 · Accepted Answer · answered Aug 25 '14 at 09:23

As you iterate over the first string's characters, you might potentially find the same character more than one time.

This means that common chars found more than one time in the first string will be counted more than one time.

This is what causing your program to calculate 58 instead of 19.

Check below some quick update to your program - it treats the duplicates in the first string.

This program calculates 19 on your 100 strings' test case.

#include<stdio.h>
#include<string.h> 

void main(){
    int n,i,j/*,count=0*/;
    int count[26] = {0};  /* counter per char */
    char s[100][101];
    scanf("%d",&n);
    for(i=0;i<n;i++){
        scanf("%s",s[i]);
    }
    int t;
    int l = strlen(s[0]);
    for(i=0;i<l;i++){
        t=0;

        /* convert char to integer - assuming lowercase char only */             
        int char_index = s[0][i] - 'a'; 

        for(j=1;j<n;j++){
            if(strchr(s[j],s[0][i])!='\0' && count[char_index] == 0){
                t++;
            }
        }
        if(t==n-1)
            count[char_index] = 1;
            /* count++; */
    }
    /* count how many chars are 1*/
    int count_n = 0;
    int index;
    for (index = 0; index < 26; index ++)
    {
        if (count[index] == 1)
            count_n ++;
    }
    printf("\n\n%d",count_n);
}

Why this program doesn't give right result when used with large strings?

1 Answers1