LeetCode：160. Intersection of Two Linked Lists

一、问题描述

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

For example, the following two linked lists:

begin to intersect at node c1.

二、思路分析

这道题跟删除尾部第n个结点差不多。只不过这里的n是两个链表的长度差，同时移动时还要考虑后一个结点是否相同。

三、代码实现

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {
        if(headA == NULL || headB == NULL) return NULL;
        int na = 0, nb = 0, n = 0, i = 1;
        //下面的while循环中,headA,headB都后移了，所以要先保存下
        ListNode* tempA = headA;
        ListNode* tempB = headB;
        
        while(headA->next != NULL) {
            na++;
            headA = headA->next;
        }
        while(headB->next != NULL) {
            nb++;
            headB = headB->next;
        }
        if(na>=nb){
            n = na - nb;
            while(i<=n){
                tempA = tempA->next;
                i++;
            }
            while(tempA != tempB){
                tempA = tempA->next;
                tempB = tempB->next;
            }
            return tempA;
        }else{
            n = nb - na;
            while(i<=n){
                tempB = tempB->next;
                i++;
            }
             while(tempA != tempB){
                tempA = tempA->next;
                tempB = tempB->next;
            }
            return tempB;
        }
    }
};