从链表中删除负值

class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next

def delete_negatives(head):
    # 处理头节点为负值的情况
    while head and head.val < 0:
        head = head.next
    
    # 处理链表中间的负值节点
    curr = head
    while curr and curr.next:
        if curr.next.val < 0:
            curr.next = curr.next.next
        else:
            curr = curr.next
    
    return head

# 创建链表：1 -> -2 -> 3 -> -4 -> 5
head = ListNode(1)
node2 = ListNode(-2)
node3 = ListNode(3)
node4 = ListNode(-4)
node5 = ListNode(5)
head.next = node2
node2.next = node3
node3.next = node4
node4.next = node5

# 删除负值节点
head = delete_negatives(head)

# 打印删除后的链表
curr = head
while curr:
    print(curr.val)
    curr = curr.next