intersection-of-two-linked-lists.java

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
        if (headA == null || headB == null) {
            return null;
        }
        
        int lenA = 0, lenB = 0;
        ListNode pA = headA, pB = headB;
        
        while (pA != null || pB!= null) {
            if (pA != null && pB != null) {
                lenA++;
                lenB++;
                pA = pA.next;
                pB = pB.next;
            } else if (pA != null) {
                lenA++;
                pA = pA.next;
            } else {
                lenB++;
                pB = pB.next;
            }
            
        }
        
        int diff = Math.abs(lenA - lenB);
        pA = headA;
        pB = headB;
        for (int i = 0; i < diff; i++) {
            if (lenA >= lenB) {
                pA = pA.next;
            } else {
                pB = pB.next;
            }
        }
        
        while (pA != null) {
            if (pA.equals(pB)) {
                return pA;
            }
            
            pA = pA.next;
            pB = pB.next;
        }
        
        return null;
    }
}