[Leetcode]160. 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:

/**
 * 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;
        ListNode curA = headA,curB = headB;
        while (curA!=null&&curB!=null){
            if (curA.next ==null&&curB.next==null&&curA!=curB)
                return null;                           //如果走到了链的尽头，而这尽头又不是交
                                                           //点，说明两条链不相交
            else if (curA==curB)                 //如果同时到交点了，就跳出循环
                break;
            if (curA.next == null)                //下面这段可能需要画图理解
                curA = headB;                      //如果两条链有交点，则curA和curB到
            else                                         //交点的距离是相同的
                curA = curA.next;
            if (curB.next == null)
                curB = headA;
            else 
                curB = curB.next;
        }
        return curA;
    }
}

• 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.