package main

type ListNode struct {
	Val  int
	Next *ListNode
}

// O(n+m) time and O(n) memory solution
// Only iterates over each list once, unlike
// the other solution which iterates twice.
/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func getIntersectionNode(headA, headB *ListNode) *ListNode {
	exists := map[*ListNode]bool{}
	for current := headA; current != nil; current = current.Next {
		exists[current] = true
	}
	for current := headB; current != nil; current = current.Next {
		if exists[current] {
			return current
		}
	}
	return nil
}