[LeetCode160] Intersection of Two Linked Lists

Write a program to find the node at which the intersection of two singly linked lists begins.

For example, the following two linked lists:

A:          a1 → a2                   ↘                     c1 → c2 → c3                   ↗            B:     b1 → b2 → b3

begin to intersect at node c1.

Notes:

• If the two linked lists have no intersection at all, return null.
• The linked lists must retain their original structure after the function returns.
• You may assume there are no cycles anywhere in the entire linked structure.

• Your code should preferably run in O(n) time and use only O(1) memory.

1. difference of two linked list lenght.

2. from the queal node, go through two linked list.

/** * 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) {        int lenA = length(headA);        int lenB = length(headB);        if(lenA == 0 || lenB ==0) return null;        int diff = Math.abs(lenA - lenB);        ListNode h1 = headA;        ListNode h2 = headB;        while(diff > 0) {            if(lenA > lenB) h1 = h1.next;            else h2 = h2.next;            diff--;        }        while(h1!=null || h2!=null){            if(h1.val == h2.val) return h1;            h1 = h1.next;            h2 = h2.next;        }        return null;    }        public int length(ListNode node){        if(node == null) return 0;        int len = 1;        while(node.next != null) {            len++;            node = node.next;        }        return len;    }}