LeetCode/160.cpp at master · nitin-maharana/LeetCode · GitHub

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/*
 * Written by Nitin Kumar Maharana
 * nitin.maharana@gmail.com
 */

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
    int findLength(ListNode* head)
    {
        int len = 0;

        while(head)
        {
            len++;
            head = head->next;
        }

        return len;
    }

    void advancePointer(ListNode **ptr, int len)
    {
        while(len--)
            (*ptr) = (*ptr)->next;
    }

public:
    ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {

        if(!headA || !headB)
            return nullptr;

        int lenA, lenB;

        lenA = findLength(headA);
        lenB = findLength(headB);

        ListNode *ptrA, *ptrB;

        ptrA = headA;
        ptrB = headB;

        (lenA < lenB) ? advancePointer(&ptrB, lenB-lenA) : advancePointer(&ptrA, lenA-lenB);

        while(ptrA && ptrB)
        {
            if(ptrA == ptrB)
                return ptrA;

            ptrA = ptrA->next;
            ptrB = ptrB->next;
        }

        return nullptr;
    }
};