链表中环的入口节点|博客系列

/*
* 查找出链表中环的入口节点
* params {ListNode} list
* returns {ListNode}	
*/
function entryNodeOfLoop(list) {
    if (!list || !list.next) return null
  	// 1.判断链表中是否有环
    let p1 = list.next,
        p2 = list.next.next
    while (p1 != p2) {
        if (p2 === null || p2.next === null) return null
        p1 = p1.next
        p2 = p2.next.next
    }
  	// 2.获取环的长度
    let temp = p1
    let length = 1
    p1 = p1.next
    while (temp != p1) {
        p1 = p1.next
        length++
    }
  	// 3.查询入口节点
    p1 = p2 = list
    while (length-- > 0) {
        p1 = p1.next
    }
    while (p1 != p2) {
        p1 = p1.next
        p2 = p2.next
    }
    return p1
}