LeetCode之Partition List

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
/*本题考查链表的遍历和尾插法（不改变相对顺序），具体方法如下：
从头开始遍历，找到小于x的结点，用尾插法加入即可。*/
class Solution {
public:
ListNode *partition(ListNode *head, int x) {
if(!head) return head;
ListNode newHead(-1);
ListNode *mark = &newHead;//小于x的结点插到mark结点后面
mark->next = head;
while(mark->next && mark->next->val < x) mark = mark->next;
ListNode *pre = mark;
if(!pre->next) return head;
ListNode *cur = pre->next;
while(cur){
if(cur->val < x){
ListNode *tmp = cur;
pre->next = cur->next;
cur = cur->next;
tmp->next = mark->next;
mark->next = tmp;
mark = mark->next;
}
else{
pre = pre->next;
cur = cur->next;
}
}
return newHead.next;
}
};