Remove Duplicates from Sorted List

Given a sorted linked list, delete all duplicates such that each element appear only once.

For example,
Given 1->1->2, return 1->2.
Given 1->1->2->3->3, return 1->2->3.

#include<stdio.h>  #include<stdlib.h>    typedef struct ListNode {      int val;      struct ListNode *next;  }ListNode;  ListNode *deleteDuplicates(ListNode *head) {    ListNode *p1=head,*p2=head;    if(head==NULL) return head;    while(p1->next!=NULL && p2!=NULL){        if(p1->next->val==p1->val) {            p2->next=p2->next->next;            p1=p2;        }        else {            p2=p1;            p1=p1->next;        }    }            return head;}void main(){    ListNode *p1,*p2,*head;    int i;    p1=(ListNode*)malloc(sizeof(ListNode));    scanf("%d",&p1->val);    for(i=1;p1->val!=0;i++){        if(i==1) head=p1;        else p2->next=p1;        p2=p1;        p1=(ListNode*)malloc(sizeof(ListNode));        scanf("%d",&p1->val);    }    p2->next=NULL;    head=deleteDuplicates(head);    for(p1=head;p1!=NULL;p1=p1->next) printf("%d\n",p1->val);}