剑指OFFER-合并两个排序的链表-PHP

题目

输入两个单调递增的链表，输出两个链表合成后的链表，当然我们需要合成后的链表满足单调不减规则。

题解

简单的合并排序。由于两个数列本来就是递增的，所以每次将两个数列中较小的部分拿过来就可以了。

代码

/*class ListNode{
    var $val;
    var $next = NULL;
    function __construct($x){
        $this->val = $x;
    }
}*/
function Merge($pHead1, $pHead2)
{
    if($pHead1 == NULL)
        return $pHead2;
    if($pHead2 == NULL)
        return $pHead1;
    $reHead = new ListNode();

    if($pHead1->val < $pHead2->val){
        $reHead = $pHead1;
        $pHead1 = $pHead1->next;
    }else{
        $reHead = $pHead2;
        $pHead2 = $pHead2->next;
    }

    $p = $reHead;
    while($pHead1&&$pHead2){
        if($pHead1->val <= $pHead2->val){
            $p->next = $pHead1;
            $pHead1 = $pHead1->next;
            $p = $p->next;
        }
        else{
            $p->next = $pHead2;
            $pHead2 = $pHead2->next;
            $p = $p->next;
        }
    }
    if($pHead1 != NULL){
        $p->next = $pHead1;
    }
    if($pHead2 != NULL)
        $p->next = $pHead2;

    return $reHead;
}