LeetCode Q160: 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:

• 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.

Solution;

A hard question at the first glance, however, it is easy if you can figure out how many node each linkedlist has.

	/**
	* 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) {
	int lenA=0;
	int lenB=0;
	ListNode* pA=headA;
	ListNode* pB=headB;
	while(pA!=NULL||pB!=NULL){
	if(pA!=NULL){
	lenA++;
	pA=pA->next;
	}
	if(pB!=NULL){
	lenB++;
	pB=pB->next;
	}
	}
	pA=headA;
	pB=headB;
	if(lenB>lenA)
	for(int i=0; i<lenB-lenA; i++)
	pB=pB->next;
	if(lenA>lenB)
	for(int i=0; i<lenA-lenB; i++)
	pA=pA->next;
	while(pA!=NULL&&pB!=NULL){
	if(pA==pB)
	return pA;
	else{
	pA=pA->next;
	pB=pB->next;
	}
	}
	return NULL;
	}
	};

view raw Q160IntersectionofTwoLinkedList.cpp hosted with ❤ by GitHub