LeetCode_Intersection of Two Linked Lists

题目链接：https://leetcode.com/problems/intersection-of-two-linked-lists/

题目：

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.

Credits:
Special thanks to @stellari for adding this problem and creating all test cases.

解题思路：跟Remove Nth Node From End of List这道题一样。把从后往前，变为从前往后。分别计算两个链表的个数，减去他们之前的差，再一起搜索。找到相同的地方，return就解决了。

class Solution {
public:
    ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {
        ListNode *Apoint = headA , *Bpoint = headB;
        int i = 0,j = 0;
        for ( ; headA != NULL; headA = headA->next)
            i++;
        for ( ; headB != NULL; headB = headB->next)
            j++;
        if( i > j) {
            for (int k = 0; k < i-j; k++) Apoint = Apoint->next;
        } else {
            for (int k = 0; k < j-i; k++) Bpoint = Bpoint->next;
        }
        while ( Apoint != Bpoint) {
            Apoint = Apoint->next;
            Bpoint = Bpoint->next;
        }
        return Apoint;
    }
};

LeetCode_Intersection of Two Linked Lists

原文：http://blog.csdn.net/vanish_dust/article/details/44150693