《leetCode-php》重排序链表

最新推荐文章于 2020-06-29 19:46:48 发布

原创最新推荐文章于 2020-06-29 19:46:48 发布 · 172 阅读

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本文介绍了一种链表数据结构的顺序重构算法，通过快慢指针找到中间节点，然后翻转后半部分链表，最后将两部分交错连接，实现原地修改链表顺序而无需改变节点值。

Given a singly linked list L: L 0→L 1→…→L n-1→L n,
reorder it to: L 0→L n →L 1→L n-1→L 2→L n-2→…

You must do this in-place without altering the nodes' values.

更改链表的顺序

For example,
Given{1,2,3,4}, reorder it to{1,4,2,3}.

找到链表的中间节点，可以使用快慢指针来获取。

<?php
class ListNode {
    public $next = null;
    public $val;
    public function __construct($val) {
        $this->val = $val;
    }
}
function reorderList($headNode) {
    $node1 = $headNode;
    $node2 = $headNode;
    //快慢指针获取中间节点
    while($node2->next->next !== null) {
        $node1 = $node1->next;
        $node2 = $node2->next->next;
    }
    $halfNode = $node1->next;
    $node1->next = null;
    //后半部分翻转
    $node3 = null;
    while ($halfNode !== null) {
        $node4 = $halfNode->next;
        $halfNode->next = $node3;
        $node3 = $halfNode;
        $halfNode = $node4;
    }
    //拼接
    $node7 = $headNode;
    while ($node3 !== null) {
        $node5 = $node7->next;
        $node7->next = $node3;
        $node6 = $node3->next;
        $node3->next = $node5;
        $node3 = $node6;
        $node7 = $node7->next->next;
    }
    return $headNode;
}
$node1 = new ListNode(1);
$node2 = new ListNode(2);
$node3 = new ListNode(3);
$node4 = new ListNode(4);
$node5 = new ListNode(5);
$node6 = new ListNode(6);
$node1->next = $node2;
$node2->next = $node3;
$node3->next = $node4;
$node4->next = $node5;
$node5->next = $node6;
$node = reorderList($node1);
while ($node !== null) {
    print $node->val."\n";
    $node = $node->next;
}