leetcode有关链表

2.2.1 Add Two Numbers
描述
You are given two linked lists representing two non-negative numbers. e digits are stored in reverse
order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.
Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
分析

跟Add Binary（见§3.4）很类似

不管是数组和链表实现相加，（二进制相加也好，）都是需要设置变量，存储进位

function f($l1,$l2){        $p1=$l1->root->next;     $p2=$l2->root->next;     $l=new Link();     $yu=0;      while($p1!=null&&$p2!=null){           $v=($p1->value+$p2->value+$yu);           $value=$v%10;           $yu=$v/10;           $l->insert($value);           $p1=$p1->next;           $p2=$p2->next;         }      while($p1!=null){            $v=($p1->value+$yu);           $value=$v%10;           $yu=$v/10;           $l->insert($value);           $p1=$p1->next;          }      while($p2!=null){            $v=($p2->value+$yu);           $value=$v%10;           $yu=$v/10;           $l->insert($value);           $p2=$p2->next;          } 

      if($yu>0) 

             $l->insert($yu);

       return $l;}

2.2.3 Partition List
描述
Given a linked list and a value x, partition it such that all nodes less than x come before nodes greater
than or equal to x.
You should preserve the original relative order of the nodes in each of the two partitions.
For example, Given 1->4->3->2->5->2 and x = 3, return 1->2->2->4->3->5.

一个维护2个链表，一个比x大，一个比x小，最终合并