6.S096 | January IAP 2014 | Undergraduate
Effective Programming in C and C++
Assignments

Sample Solution to Assignment 2, Problem 1

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#include <"list.h">
 
#include <stdio.h>
#include <stdlib.h>
 
struct List_node_s {
  List_node *next;
  int value;
};
 
List empty_list( void ) {
  return (List) { .length = 0, .front = NULL };
}
 
List_node* create_node( int value ) {
  List_node *new_node = malloc( sizeof( List_node ) );
  new_node->value = value;
  new_node->next = NULL;
  return new_node;
}
 
void list_append( List *list, int value ) {
  if( list->front == NULL ) {
    list->front = create_node( value );
  } else {
    List_node *p = list->front;
    for( size_t i = 1; i < list->length; ++i, p = p->next );
    p->next = create_node( value );
  }
  ++list->length;
}
 
void list_delete_from_front( List *list, int  value ) {
  List_node *front = list->front;
  while( front != NULL && front->value == value ) {
    list->front = front->next;
    --list->length;
    free( front );
    front = list->front;
  }
}
 
void list_delete( List *list, int value ) {
  list_delete_from_front( list, value );
  if( list->front == NULL ) {
    return;
  }
 
  List_node *prev = list->front;
  List_node *p = list->front->next;
 
  while( p != NULL ) {
    if( p->value == value ) {
      prev->next = p->next;
      free( p ); --list->length;
      p = prev->next;
    } else {
      prev = p;
      p = prev->next;
    }
  }
}
 
void list_insert_before( List *list, int insert, int before ) {
  if( list->front != NULL && list->front->value == before ) {
    List_node *new_node = create_node( insert );
    new_node->next = list->front;
    list->front = new_node;
    ++list->length;
  } else {
    List_node *prev = list->front;
    List_node *next = list->front->next;
    while( next != NULL ) {
      if( next->value == before ) {
        prev->next = create_node( insert );
        prev->next->next = next;
        ++list->length; return;
      }
      prev = next;
      next = next->next;
    }
  }
}
 
 
void list_apply( List *list, int (*function_ptr)( int) ) {
  for( List_node *p = list->front; p != NULL; p = p->next ) {
    p->value = (*function_ptr)( p->value );
  }
}
 
int list_reduce( List *list, int (*function_ptr)(int, int) ) {
  if( list->front == NULL ) {
    return 0;
  }
 
  int result = list->front->value;
 
  for( List_node *p = list->front->next; p != NULL; p = p->next ) {
    result = (*function_ptr) ( result, p->value );
  }
 
  return result;
}
 
void list_print( List list ) {
  if( list.front == NULL ) {
    printf( "{}\n" );
  } else {
    printf( "{ " );
 
    List_node *p = list.front;
    size_t length = list.length;
 
    while( p->next != NULL && length > 0 ) {
      printf( "%d -> ", p->value );
      p = p->next; --length;
    }
    printf( "%d }\n", p->value );
 
    if( length != 1 ) {
      printf( "Error: badly formed list.\n" );
      exit( EXIT_FAILURE );
    }
  }
}
 
 
void list_clear( List *list ) {
  List_node *front = list->front;
  size_t length = list->length;
 
  while( front != NULL && length > 0 ) {
    List_node *next = front->next;
    free( front );
    front = next;
    --length;
  }
 
  if( length != 0 ) {
    printf( "Error: failed to clean up list properly.\n" );
    exit( EXIT_FAILURE );
  }
}

Below is the output using the test data:


list:
 1: OK [0.002 seconds] OK!
 2: OK [0.004 seconds] OK!
 3: OK [0.035 seconds] OK!
 4: OK [2.175 seconds] OK!
 5: OK [0.133 seconds] OK!
 6: OK [0.305 seconds] OK!
 7: OK [0.061 seconds] OK!
 8: OK [0.213 seconds] OK!
 9: OK [0.002 seconds] OK!
10: OK [1.054 seconds] OK!

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January IAP 2014
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