GATE CSE
First time here? Checkout the FAQ!
x
+2 votes
109 views
Write a constant time algorithm to insert a node with data $D$ just before the node with address $p$ of a singly linked list.
asked in DS by Veteran (289k points)   | 109 views
// node is a struct containing an int and next pointer
void insert(int D, node* p){
	node* temp = (node*)malloc(sizeof(node));
	temp->next = p->next; // make temp point to the node where p was pointing
	p->next = temp; // attach node temp next to node p 
	/*till this point it is simialr to inserting node after a node
	whose pointer p is given. Now change the data of both nodes p and temp to get desired result*/
	temp->data = p->data; // copy the data of current node to new node
	p->data = D;
}
	

1 Answer

+9 votes
Best answer
let A,B,C,D,E,F be the data ..
A---> B ----> C----> E ---->F
let pointer to E be p..
a node with data D has to be inserted before E..
i ll do one thing , add D just after node E .. it ll take constant time..
Pnext --->Address_of_D
Address_of_D.next------> Address_of_F

A---> B ----> C----> E -----> D---->F

take a temporary variable and swap the value E and D..
temp = p.data
p.data= p.next.data
p.next.data= temp
now linked list wil look like ..
A---> B ----> C----> D-----> E ---->F
still one more work left.. now pointer p pointing to D so increment pointer p to point data E..
p= p--->next
answered by Veteran (46.2k points)  
selected by
Your logic is awesome ! Try for part a too !


Top Users Jul 2017
  1. Bikram

    5368 Points

  2. manu00x

    3092 Points

  3. Arjun

    1924 Points

  4. joshi_nitish

    1898 Points

  5. Debashish Deka

    1874 Points

  6. pawan kumarln

    1454 Points

  7. Tesla!

    1390 Points

  8. Hemant Parihar

    1314 Points

  9. Shubhanshu

    1136 Points

  10. Arnab Bhadra

    1124 Points


24,141 questions
31,143 answers
70,892 comments
29,467 users