IntersectionOfTwoLinkedLists.java

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {

    // TC : O(l1 + l2)
     public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
         int lenA =  length(headA);
         int lenB =  length(headB);
         if(lenA > lenB){
             int diff = lenA -lenB;
             while(diff>0){
                 headA = headA.next;
                 diff--;
             }
         } else{

             int diff = lenB -lenA;
             while(diff>0){
                 headB = headB.next;
                 diff--;
             }
         }
         while(headA !=null && headB!=null){
             if(headA == headB){
                 return headA;
             }
             headA = headA.next;
             headB = headB.next;
         }

         return null;
     }

     private int length(ListNode head){
         int len = 0;
         while(head!=null){
             head = head.next;
             len++;
         }
         return len;
     }

    // TC : O(l1+l2)
    public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
        ListNode a = headA;
        ListNode b = headB;

        while(a!=b){
            if(a == null){
                a = headB;
            } else{
                a = a.next;
            }


            if(b == null){
                b = headA;
            } else{
                b = b.next;
            }
        }

        return a;

    }
}