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Deletion of last node in singly link list

Now we will see how to delete node at last position in singly link list.

Algorithm to delete last node in singly link list:

  • Set TEMP = START
  • If START != NULL
    • If list has only one node i.e. [START->NEXT == NULL ]
      • Set START = NULL
    • Else
      • Traverse the list so that TEMP points to second last node
      • Make second last node point to nothing i.e. [TEMP->NEXT = NULL]
    • End If
  • End If

Function to delete last node in singly link list:

  

int deleteLast(NODE **start){
 NODE *temp = *start;
 int info = -1;
 if(*start == NULL){
  printf("\nNo nodes exists in the list");
 }
 else if((*start)->next == NULL){
  info = (*start)->info;
  free(*start);
  *start = NULL;
 }
 else{
  while(temp->next->next != NULL){
   temp = temp->next;
  }
  info = temp->next->info;
  free(temp->next);
  temp->next = NULL;
 }
 return info;
}
 

Program to delete last node in the singly link list:

  

#include <stdio.h>
#include <malloc.h>

struct node{
 int info;
 struct node *next;
};
typedef struct node NODE;

void insertAtFirst(NODE **, int);
int deleteLast(NODE **);
void traverse(NODE **);

int main(){
 
 NODE *start = NULL;
 
 insertAtFirst(&start, 4);
 insertAtFirst(&start, 5); 
 traverse(&start);
 deleteLast(&start);
 printf("\n");
 traverse(&start);

 return 0;
}


int deleteLast(NODE **start){
 NODE *temp = *start;
 int info = -1;
 if(*start == NULL){
  printf("\nNo nodes exists in the list");
 }
 else if((*start)->next == NULL){
  info = (*start)->info;
  free(*start);
  *start = NULL;
 }
 else{
  while(temp->next->next != NULL){
   temp = temp->next;
  }
  info = temp->next->info;
  free(temp->next);
  temp->next = NULL;
 }
 return info;
}

void insertAtFirst(NODE **start, int info){
 NODE *ptr = (NODE*) malloc(sizeof(NODE));
 ptr->info = info;
 ptr->next = *start;
 *start = ptr; 
}

void traverse(NODE **start){
 NODE *temp;
 temp = *start;
 while(temp != NULL){
  printf("%d  ", temp->info);
  temp = temp->next;
 }
}
Output: 
5  4
5

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