160. Intersection of Two Linked Lists （求两个链表的交集）

逃离我推掉我的手 2022-07-15 01:20 102阅读 0赞

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.

/**
     * 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 lengthA = 0, lengthB = 0;
    		ListNode a = headA, b = headB;
    		while (a != null) {
    			lengthA++;
    			a = a.next;
    		}
    		while (b != null) {
    			lengthB++;
    			b = b.next;
    		}
    		a = lengthA <= lengthB ? headA : headB;
    		b = lengthA <= lengthB ? headB : headA;
    		int dif = Math.abs(lengthA - lengthB);
    		while (dif-- > 0)
    			b = b.next;
    		while (a != null && b != null && a != b) {
    			a = a.next;
    			b = b.next;
    		}
    		return a;
        }
    }