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

linkedlistintersect.cpp

/**
 * 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 || !headB) {
            return NULL;
        }
        int lenA = getListLen(headA);
        int lenB = getListLen(headB);
        
        // Attempt to match the list heads
        if (lenA > lenB) {
            headA = advanceList(headA, lenA - lenB);
        } else if (lenA < lenB) {
            headB = advanceList(headB, lenB - lenA);
        }
        
        // Heads should be matched
        while(headA != NULL && headB != NULL) {
            if (headA == headB) {
                return headA;
            }
            headA = headA->next;
            headB = headB->next;
        }
        return NULL;
    }

    int getListLen(ListNode *head) {
        int length = 0;
        while(head) {
            head = head->next;
            length++;
        }
        return length;
    }

    ListNode *advanceList(ListNode *head, int len) {
        for(int i = 0; i < len; i++){
            head = head->next;
            if (!head) {
                return NULL;
            }
        }
        return head;
    }
};