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# 1  
Old 10-22-2014
Script List
I am looking at these two scripts and was wondering what would the list look like in each?

Code:
int main()
{
        int i;
        int rV = 0;
        List l = NULL;
        char* input[] = { "06", "24", "3" };
        sNode *s, *t;

        for( i=0; i<3; ++i )
        {
                t = (sNode*)malloc( sizeof( sNode ));
                if( t == NULL )
                {
                        fprintf( stderr, "Couldn't get memory for a node!  Exiting." );
                        rV = 1;
                        break;
                }
                t->data = input[i];
                t->next = l;
                l = t;
        }

        /* What does this list look like here? */

        s = l;
        while( s != NULL )
        {
                t = s->next;
                free( s );
                s = t;
        }

        return rV;
}

Code:
import sys

main( args=sys.argc ) :

        L = [24, None]

        t = [13, None]
        t[1] = L
        L = t

        t = [28, None]
        t[1] = L[1]
        L[1] = t

        t = [3, None]
        p = L
        while p != None :
                q = p
                p = p[1]

        if p == L :
                L = t
        else :
                q[1] = t

        print L

# 2  
Old 10-22-2014
Your first program is incomplete, List and sNode aren't defined anywhere, which is why it looks so weird. I can probably assume list and snode are the same, so they look like this:

Code:
typedef struct sNode {
        struct sNode *next;
        char *data;
};

#define List sNode

It is a linked list, where each element holds a reference to the next one, or a NULL reference if the list is ending.

After the first loop it looks like this:

Code:
L -> ["06"] -> NULL

Second loop:
Code:
L -> ["24"] -> ["06"] -> NULL

etc.

You can see how they create a new node with "malloc", set it to point to the old node t->next=l; and then make the root point to it l=t;

I cannot grasp that python code at all, so I can't tell how or if it's related to this, though I suspect python doesn't actually have a linked list -- it's a higher level language, operating above the level where you'd know or care how it remembers what elements go where.
This User Gave Thanks to Corona688 For This Post:
totoro125
# 3  
Old 10-22-2014
Quote:
Originally Posted by Corona688
Your first program is incomplete, List and sNode aren't defined anywhere, which is why it looks so weird. I can probably assume list and snode are the same, so they look like this:

Code:
typedef struct sNode {
        struct sNode *next;
        char *data;
};

#define List sNode

It is a linked list, where each element holds a reference to the next one, or a NULL reference if the list is ending.

After the first loop it looks like this:

Code:
L -> ["06"] -> NULL

Second loop:
Code:
L -> ["24"] -> ["06"] -> NULL

etc.

You can see how they create a new node with "malloc", set it to point to the old node t->next=l; and then make the root point to it l=t;

I cannot grasp that python code at all, so I can't tell how or if it's related to this, though I suspect python doesn't actually have a linked list -- it's a higher level language, operating above the level where you'd know or care how it remembers what elements go where.
Thank you! That helps a lot.
I am a little confused on this one also. What would this display?

Code:
#include <stdlib.h>
#include <string.h>
#include <stdio.h>

#define TABLE_SIZE  7
#define NUM_INPUTS  7

int hash( char *s )
{
        return strlen( s ) % TABLE_SIZE ;
}

typedef struct entry
{
        char *key;
        int     val;
        struct entry *next;
} entry;

entry* table[ TABLE_SIZE ] = { NULL };

void insert( char *s, int v )
        /* this insert is NOT checking for duplicates.  :/ */
{
        int h = hash( s );
        entry *t = (entry*) malloc( sizeof( entry ));

        t->key = s;
        t->val = v;
        t->next = table[h];
        table[h] = t;
}

void clean_table()
{
        entry *p, *q;
        int i;

        for( i=0; i<TABLE_SIZE; ++i )
        {
                for( p=table[i]; p!=NULL; p=q )
                {
                        q = p->next;
                        free( p );
                }
        }       // for each entry
}       // clean_table


int main()
{
        char* keyList[] = { "Jaga", "Jesse", "Cos", "Kate", "Nash", "Vera",
                "Bob" };

        int valList[] = { 24, 78, 86, 28, 11, 99, 38 };

        int i;

        for( i=0; i<NUM_INPUTS; ++i )
                insert( keyList[i], valList[i] );

        /* what does the table look like here? */

        clean_table();

        return( 0 );
}

# 4  
Old 10-23-2014
This is a simplified representation of how the table array would look:

Code:
table[0] (Undefined)
table[1] (Undefined)
table[2] (Undefined)
table[3] => {"Bob", 38} -> {"Cos", 86}
table[4] => {"Vera", 99} -> {"Nash", 11} -> { "Kate", 28 } -> {"Jaga", 24 }
table[5] => {"Jesse", 78}
table[6] (Undefined)

Last edited by Chubler_XL; 10-23-2014 at 01:39 AM.. Reason: Values inserted at front of lists - not end
This User Gave Thanks to Chubler_XL For This Post:
totoro125
# 5  
Old 10-25-2014
Quote:
Originally Posted by Chubler_XL
This is a simplified representation of how the table array would look:

Code:
table[0] (Undefined)
table[1] (Undefined)
table[2] (Undefined)
table[3] => {"Bob", 38} -> {"Cos", 86}
table[4] => {"Vera", 99} -> {"Nash", 11} -> { "Kate", 28 } -> {"Jaga", 24 }
table[5] => {"Jesse", 78}
table[6] (Undefined)

Thank you ^^ but can you explain how you got that?
Also, I was wondering if it was possible to write a function that takes a key and a reference to an integer and fills in the reference with the appropriate value, while returning true? If possible, how would you write it?
Last edited by totoro125; 10-25-2014 at 11:42 PM..
# 6  
Old 10-26-2014
entry* table[ TABLE_SIZE ] = { NULL }; this statement initializes the "table" array as a TABLE_SIZE (7) element array with NULL pointers. In C arrays are indexed from zero so we end up with:

Code:
table[0] (Undefined)
table[1] (Undefined)
table[2] (Undefined)
table[3] (Undefined)
table[4] (Undefined)
table[5] (Undefined)
table[6] (Undefined)

I use (Undefined) here, as the table array element contains a NULL pointer. In the context of this code (empty) could be a better analogy.

The insert code calculates a hash value of the input string being the length of the string modulo the TABLE_SIZE (7). This is a pretty simple hash which results in strings of various lengths being inserted into the table array as follows:

Code:
table[0] ~ lengths     7, 14, 21, 28, etc
table[1] ~ lengths 1,  8, 15, 22, 29, etc
table[2] ~ lengths 2,  9, 16, 23, 30, etc
table[3] ~ lengths 3, 10, 17, 24, 31, etc
table[4] ~ lengths 4, 11, 18, 25, 32, etc
table[5] ~ lengths 5, 12, 19, 26, 33, etc
table[6] ~ lengths 6, 13, 20, 27, 34, etc

Looking at this code in the insert function:

Code:
        t->key = s;
        t->val = v;
        t->next = table[h];
        table[h] = t;

we can see that each element of table is a linked list and new values are inserted at the front of the list.

So "Jaga" is inserted into the table[4] list first, then later "Kate" is inserted in front of "Jaga" then "Nash", and so forth.

Here is the update code you requested:

Code:
int update( char *s, int v )
/* Update 1st found entry with a key matching s assign new val of v
    returns 1 if an entry is updated and 0 otherwise */
{
        int h = hash( s );
        entry *t;

        for(t=table[h]; t!=NULL; t=t->next)
            if (!strcmp(s, t->key)) {
                 t->val = v;
                 return 1;
            }
        return 0;
}

Last edited by Chubler_XL; 10-26-2014 at 05:30 PM..
This User Gave Thanks to Chubler_XL For This Post:
totoro125
# 7  
Old 10-26-2014
Quote:
Originally Posted by Chubler_XL
entry* table[ TABLE_SIZE ] = { NULL }; this statement initializes the "table" array as a TABLE_SIZE (7) element array with NULL pointers. In C arrays are indexed from zero so we end up with:

Code:
table[0] (Undefined)
table[1] (Undefined)
table[2] (Undefined)
table[3] (Undefined)
table[4] (Undefined)
table[5] (Undefined)
table[6] (Undefined)

I use (Undefined) here, as the table array element contains a NULL pointer. In the context of this code (empty) could be a better analogy.

The insert code calculates a hash value of the input string being the length of the string modulo the TABLE_SIZE (7). This is a pretty simple hash which results in strings of various lengths being inserted into the table array as follows:

Code:
table[0] ~ lengths     7, 14, 21, 28, etc
table[1] ~ lengths 1,  8, 15, 22, 29, etc
table[2] ~ lengths 2,  9, 16, 23, 30, etc
table[3] ~ lengths 3, 10, 17, 24, 31, etc
table[4] ~ lengths 4, 11, 18, 25, 32, etc
table[5] ~ lengths 5, 12, 19, 26, 33, etc
table[6] ~ lengths 6, 13, 20, 27, 34, etc

Looking at this code in the insert function:

Code:
        t->key = s;
        t->val = v;
        t->next = table[h];
        table[h] = t;

we can see that each element of table is a linked list and new values are inserted at the front of the list.

So "Jaga" is inserted into the table[4] list first, then later "Kate" is inserted in front of "Jaga" then "Nash", and so forth.

Here is the update code you requested:

Code:
int update( char *s, int v )
/* Update 1st found entry with a key matching s assign new val of v
    returns 1 if an entry is updated and 0 otherwise */
{
        int h = hash( s );
        entry *t;

        for(t=table[h]; t!=NULL; t=t->next)
            if (!strcmp(s, t->key)) {
                 t->val = v;
                 return 1;
            }
        return 0;
}

Thank you so much! This helps a lot =D
One last thing, would you happen to know how to run the python code? I know it's incomplete but I am not sure what to add so I can make it run and see the output.
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