<?php

class ListNode {

public $val = 0;

public $next = null;

function __construct($val = 0, $next = null) {

$this->val = $val;

$this->next = $next;

}

}

/**

* @param ListNode $headA

* @param ListNode $headB

* @return ListNode

*/

function getIntersectionNode($headA, $headB) {

$pA = $headA;

$pB = $headB;

$a_len = getNodeListLength($pA);

$b_len = getNodeListLength($pB);

$len = abs($a_len - $b_len);

if($a_len >= $b_len){

//A链表较长，则A链表指针先移动$a_len-$b_len位

while ($len > 0){

$pA = $pA->next;

$len--;

}

}else{

//同理则B链表先移动

while ($len > 0){

$pB = $pB->next;

$len--;

}

}

while($pA !== null && $pB !== null && $pA !== $pB){

$pA = $pA->next;

$pB = $pB->next;

}

if($pA === null || $pB ===null){

return null;

}else{

return $pA;

}

}

function getNodeListLength($head)

{

$i = 0;

while ($head !== null){

$head = $head->next;

$i++;

}

return $i;

}