链表划分

LeetCode 86.Partition List
已知链表头节点指针head与数值X,将所有小于x的节点放在大于或等于x的节点前，且保持这些节点的原来的相对位置

算法：巧用两个临时头节点

class Solution{
public:
    ListNode *partition(ListNode *head,int x){
        ListNode less_head(0);
        ListNode more_head(0);
        ListNode *less_ptr = & less_head;
        ListNode *more_ptr = & more_head;//对应指针指向这两个头节点
        while(head){
            if(head->val < x){
                less_ptr->next = head;
                less_ptr = less_ptr->next;
              }
            else{
                more_ptr->next = head;
                more_ptr = more_ptr->next;
                    }
             head = head->next;//遍历链表
         }
        less_ptr->next =more_head.next;
        more_ptr->next = NULL;
        return less_head.next;//less_head的next节点即为新链表头节点，返回
    }
}

测试

int main(){
      ListNode a(1);
      ListNode b(4);
      ListNode c(3);
      ListNode d(2);
      ListNode e(5);
      ListNode f(2);
      a.next = &b;
      b.next = &c;
      c.next = &d;
      d.next = &e;
      e.next = &f;
      Solution solve;
      ListNode *head =solve.partition(&a,3);
      while(head){
          printf("%d\n,head->val");
          head = head->next  ;    
}
 
}