/*
 * @lc app=leetcode id=160 lang=java
 *
 * [160] Intersection of Two Linked Lists
 */

// @lc code=start
/**
 * 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 la = len(headA), lb = len(headB);
        ListNode cura = headA, curb = headB;
        if(la < lb) {
            // move curB
            for(int i=0; i<lb-la; i++) {
                curb = curb.next;
            }
        } else {
            // move curA
            for(int i = 0; i<la-lb; i++) {
                cura = cura.next;
            }
        }
        ListNode r = null;
        while(cura!=null) {
            if(cura == curb) {
                r = cura;
                break;
            }
            cura = cura.next;
            curb = curb.next;
        }
        return r;
    }

    private int len(ListNode head) {
        int l = 0;
        while(head != null) {
            l++;
            head = head.next;
        }
        return l;
    }
}
// @lc code=end