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// @Title: 两个链表的第一个公共节点 (两个链表的第一个公共节点  LCOF)
// @Author: 15816537946@163.com
// @Date: 2022-02-13 19:42:20
// @Runtime: 28 ms
// @Memory: 7 MB
/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func getIntersectionNode(headA, headB *ListNode) *ListNode {
    if headA == nil ||  headB == nil {
        return nil
    }

    aCnt, bCnt:=0,0
    curA, curB := headA, headB  
    for curA != nil {
        curA = curA.Next
        aCnt++
    }
    for curB != nil {
        curB = curB.Next
        bCnt++
    }
    curA, curB = headA, headB
    if aCnt > bCnt {
        for aCnt !=bCnt {
            curA = curA.Next
            aCnt--
        }
    } else {
        for aCnt != bCnt {
            curB = curB.Next
            bCnt--
        }
    }

    for curA!= nil && curB != nil {
        if curA == curB {
            return curA
        }
        curA = curA.Next
        curB = curB.Next
    }

    return nil
}