LeetCode：160. Intersection of Two Linked Lists

一、問題描述

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

這道題跟刪除尾部第n個結點差不多。只不過這裏的n是兩個鏈表的長度差，同時移動時還要考慮後一個結點是否相同。

三、代碼實現

/**
 * 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循環中,headA,headB都後移了，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;
        }
    }
};